Some questions, and looking for suggestions on which mods I should use now.

I saw that it was possible to build bases, I guess I was just being paranoid about how long I would have to do so. If it was as tight as 10 minutes with two heavy oxygen tanks, I think people would be complaining about that instead of recommending the mod. I've downloaded Galacticraft and the Galacticraft Planets addon (and of course the Micdoodle Core).

I've gone ahead and downloaded Rei's minimap for now, but I'm still hoping for more details to help me decide between Project-E and some of the competing mods, and it's less important when I'm using GregTech to get worldgen iridium ore, but I'm still curious about the best way to get iridium ore using only IC2exp (I know I have to find some in a dungeon chest first, but after that would it be easier/faster to look for more dungeon chests or to scan it and use a mass fabricator and replicator?).

Side note: the apartment complex where I live will be shutting down the telecommunications for maintenance in a little under an hour (and possibly keeping them down for up to 7 hours ), so I won't be able to respond to other suggestions or questions until after that. I plan to do some other things in the meantime, but if I get too tired or (unlikely) run out of other things to do, I might start an offline game with just the mods I've downloaded so far, instead of waiting for more suggestions.

Apparently my internet connection is still up for now (which I'm a little confused about).

I think you might be mistaken about not being able to download EER yet. The download link in the first post of the EER thread 404s, but try the link in this post of the thread: http://www.minecraftforum.net/…xchange-reborn?comment=31

I'm still holding off on downloading it myself in case somebody can explain how and why it's better than competing mods like AetherCraft or Balanced Exchange (or why one of those is better, as the case may be).

Okay, there's one argument against using any of them, thank you for that.

I'm having some trouble getting Galacticraft Planets working at the moment, though - with it enabled in MultiMC, Minecraft crashes with a message about entity id 174 already being defined - I found that mars.conf by default uses that id for the Sludgeling, but I don't know which other mod is defining something with that id (from what I can find, entity id 174 isn't used by vanilla Minecraft), or how to get a list of which entity ids have been defined (including by installed mods) so that I can find some unused entity ids to put in mars.conf. A way to get a list of biome ids would be good too - I don't currently plan to use Biomes O Plenty (I'm using New Dawn instead), but I ran into some biome id conflicts a while ago when I tried to install both BoP and Twilight Forest.

Quote from Chocohead

Pretty sure NEI has the option to dump free biome and entity IDs (it used to do block and item IDs too), so you could always do that. God was it useful back when we had ID conflicts (and bugs that meant any world generated block needed to be below ID 256).

NEI tools menu shows dump buttons for biomes, blocks, enchantments, items, item panel details, and potions, but there's nothing for creatures/entities as far as I can tell.

I got it working by counting down from 255 for the entity ids in mars.conf.

Edit: I started my survival game last night, but I came across a structure right near my initial spawn point that had some densely-populated chests in it, which would have been balanced by the indestructible (at least as far as I could tell) monster spawners nearby if I wasn't playing in peaceful mode. It looked like some ruins, so I pulled the Ruins mod, but that didn't get rid of it, so I also pulled the New Dungeons mod which did eliminate it. (I re-created my world both times using the New Dawn world type and my username as the random seed)

Further Edit (presuming that post bumps are frowned upon): I ran into some trouble with Black Granite from GregTech - on my 4k TV it's very hard to see, even with the contrast set to 100 and the Gammabright mod installed and cranked up to 1500% (which is partly an issue with the quality of my TV). I figured out how to disable black granite in WorldGeneration.cfg, though I've come across a couple of other things I'm not happy about (which I don't see easy ways to deal with via config):
1. NEI won't show me the recipe for the standard IC2 solar panel, so I'm guessing it's disabled with GregTech installed, but that means I won't be able to build Compact Solars.
2. I read in the Q/A of the main GregTech post that GT machines can't take power via IC2 cables or from IC2 energy storage blocks. I'll take Greg's word for it that supporting them would cause lag, but I have to wonder whether GT really still qualifies as an IC2 addon when that conflict exists.

At the moment, I'm also a little overwhelmed by the number of materials and machines added by GregTech: e.g. 77 different plate types I can use to make a file? I'm also puzzled that I apparently could make a file with lead plates (according to NEI at least), but not with tin plates. Given enough time, I could probably get used to that, though.

I've also come across a detail of the New Dawn mod that I'm not entirely happy about: the beaches tend to have much less accessible sand (i.e. that doesn't require getting into the water to dig out) compared to the default worldgen's beach biome.

After my above edits, I removed GregTech from my list, plus a few others I decided weren't worth it, like MAtmos and the shader pack, and started a new game. Now I'm not so sure Forestry was such a good suggestion for going with IC2 - the electrical engine from it doesn't seem to work with the latest version of IC2 (at least connected via cables, I haven't tried putting my energypack into it), and based on recent posts in the Forestry thread at minecraftforum.net, it seems to have switched from using MJ to using RF, which means that BuildCraft engines probably wouldn't work either.

I guess the Buildcraft wiki is out of date as well then.
Given that I've already built an mfsu and nuclear reactor, I was hoping I'd be able to use the electrical engine to power a thermionic fabricator and then a managed multifarm of oak and birch trees, since Millenaire village projects tend to require a lot of those kinds of wood. Since that doesn't work (when I tried it, it intermittently showed a message about being out of fuel, but I thought the electrical engine only took EU, not fuel), perhaps you could suggest an engine type to build to power such a fabricator, preferably one that doesn't require a lot of extra machines to process items into usable fuel, even if it's less efficient.

Installing the latest versions of those didn't seem to work at first, but then I remembered (or maybe realized - not sure whether I actually knew about it before) that all BC/Forestry engines require a redstone signal to run, not just the redstone engine . However, when I went near a village, Millenaire started spamming my chat with error messages, so I rolled back to the versions I had been using before (BC 6.0.18, Forestry 3.1.1.4) and restored a backup save I had done just beforehand, and with those and a lever to activate the electrical engine, it worked fine.

Okay, I'll try 6.0.0pb2 (I had been using 5.3, looks like the betas came out a few days after I had downloaded that), and while I'm at it, I'll go through my other mods to see if newer versions are available.

Forestry was an excellent suggestion - multifarms are handy for producing the wood that the Millenaire villages want, though I discovered that it doesn't work too well to try to do two types of tree on one multifarm - I should have made two small multifarms instead of one big one. I also like the Miner's and Digger's backpacks, though I discovered that tropical hives (needing for eventually getting silk to make woven backpacks with more capacity) are rarer than intended, but the developer is aware of that now and planning to fix it (in the meantime, I set up a molecular transformer recipe for converting string to silk, although I later discovered I could have used the uncrafting table from Twilight Forest). I didn't bother trying the "rubber plantation" option available for multifarms, because stickreed and a crop harvestor with cropnalyzer worked great - I've got a few thousand rubber that I haven't used yet.

As far as railcraft, I've only used the railcraft blast furnace so far (since it's faster than the IC2 blast furnace).

I've tried galacticraft for a bit, and it looks like two heavy oxygen tanks would last me about an hour and half real time, which is plenty. However, I'm disappointed that the alien villages haven't really been developed yet, and I don't like the idea of having to fight an evolved creeper boss to get the tier 3 rocket schematic. Also, most of the new ore types available on other planets don't seem to have much use outside of building better rockets and rocket-related machines.

There are a few other things I'd like to be able to do, though:
1. Have an item (possibly from an IC2 addon, preferably other than GregTech, and at least as much capacity as an Energypack) that could recharge my tools without taking up the chest slot, so that I could just keep my hazmat suit on all the time. (e.g. that works while sitting in my inventory, or possibly uses an extra slot added by another mod like Tinkers' Construct)
2. Control other machines based on how full my mfsu (or mfe etc.) is. (e.g. turn off my nuclear reactor to save uranium if my mfsu is already mostly full, then turn it back on when it's low, or turn off a power-hungry machine like a mass fabricator when it's low, then turn it back on when it's full)
3. Automatically breed cows and harvest the leather (mainly for making bookcases to sell to Millenaire villages).

I'd prefer it if Thaumcraft had a tutorial I could read before downloading (as opposed to getting the details from an in-game item), but I noticed that there's an IC2/Thaumcraft cross-functionality mod called "Electro-Magic Tools", so I've downloaded that (along with the requirements Thaumcraft and Baubles, and Magic Bees while I was at it).

As far as the mfsu comparator, I thought of that, but I haven't found documentation of which EU levels translated to which comparator levels, so I wasn't sure it even supported that. If there is some documentation on that, it would make it easier for me to figure out how long to make the line of redstone.