A question about building a reactor or 2

Pretty sure Nuclear Control is all you need. Reactor gets hot, nuclear monitor puts out redstone signal, that touches reactor, it turns off.

Do you want a reactor that gets turned on and off automatically as needed or one that can run continuously for a full cycle? The first part of your message seems to imply you want the first type, but the last part seems to imply you want the second type.

As far as what it can power, it generates EU (albeit indirectly if using the fluid-style 5x5x5 reactor), which can power IC2 machines and Galacticraft machines directly, as well as AE2 chargers and inscribers. Most other AE2 devices require AE2 power via AE2 cables, but you can use an Energy Acceptor to convert from IC2 power to AE2 power. I don't think Buildcraft includes a converter for its machines, but if you have Forestry installed, you can build Electrical Engines that convert EU to RF (presuming you're running Minecraft 1.7.10 and the latest versions of Buildcraft and Forestry), and there's also the Power Converters mod. I haven't used Thermal Expansion so I don't know if it adds any converter blocks for handling EU, but afaik it uses RF, so a Forestry Electrical Engine or Power Converters RF producer would probably work for its machines.

Quote from V497

I would like to build some reactors that turn on and off automatically as needed and also for an alarm to trigger all over my facility should things go bad with the reactors and my facility is pretty big so any help would be greatly appreciated:

To make the reactor turn off when it reaches a certain heat and turn back on once it cools down, I suggest you build an RS Latch with two thermal monitors feeding it - one set to the temperature you want the reactor to shut off at feeding the "R" input of the RS latch and one set to just above zero with a NOT gate feeding the "S" input of the RS latch. You might also want to set up an AND gate between the "Q" output of the RS latch and a lever, so that you can make sure it stays off while you're setting it up initially or when the time comes to put new fuel rods in. The main Minecraft wiki has designs for those memory and logic circuits that don't require Project Red or similar (although they often require some space to set up).

As far as the alarm, Nuclear Control has you covered there too: it provides a Howler Alarm and an Industrial Alarm. You can use a third thermal monitor set 5-10% higher than the shutoff temperature and connect redstone from that to one or more of those alarms.

Quote from V497

also the Minecraft version I am using is v1.6.4 due to the fact that most of my mods only work in Minecraft version 1.6.4

I think you might be mistaken about that. A lot of mods have 1.7.10 versions now, including the 6 you listed in your initial post. Perhaps you could list the ones you haven't found 1.7.10 versions for, and I could double-check. However, if you've been playing your 1.6.4 world for a while, I can understand you being reluctant to upgrade. Anyway, I think the 1.6.4 version of Buildcraft uses MJ for power, but the 1.6.4 Forestry Electrical Engine would convert EU to MJ for BC/Forestry devices (though not TE devices), and the 1.6.4 version of the Power Converters mod probably includes an MJ producer (for BC/Forestry devices) as well as an RF producer (for TE devices).