Well, to be quite honest... in my last map I built specifically for MOX from the outset, and actually never got around to it.
I started with Thermal Expansion, which was just out fresh at the time, to get my basic needs covered. Once I had a tesseract connected quarry going and started to get real resource income, I built myself an IC2 workshop (a recycling system for the quarry output to start with, and then going from there). It was to be driven by a big underground reactor core which I dubbed "The Heart of the Mountain". It was made up of eight of my three-chamber MOX reactors, for a total output of up to 5400 EU/t. Except that I started off running them on uranium because I didn't have MOX fuel yet.
I have never before in my Minecraft career built something that incredibly expensive! Three full-size 64x64 ocean quarries had run their course by the time I had enough diamonds, and that included processing every last piece of coal into diamonds as well. And I actually managed to use up all of the iron, too. In parallel to that I was using manual digging by means of Gravisuite advanced diamond drill and a heightband targeted IC2 miner as well as trading with other players to supply myself with lead, copper and tin (the custom oregen meant that the quarries produced none of that). It took me weeks of gameplay.
All during that time, I used the first sub-reactor I built to power my workshop. Well, initially it was a trio of geothermals, but as soon as the first reactor was complete, I switched to nuclear power. The 135 EU/t were easily enough to cover my needs, especially since bulk ore processing still ran through my TE setup and the thermal centrifuge isn't worth using for ore anyway.
I eventually finished building all those reactors, as well as the assorted luxury infrastructure that came after them because I could (four MFSUs, a teleporter station leading to my various friends' bases etc). I did have a full massfab/replicator setup with some 800 buckets stored up, too. But, even though I at one point ran the Heart in full power mode under uranium (still a respectable 1080 EU/t), I just really didn't need all that much EU/t. And over the entire time of building all this and generating all that UU-matter, I managed to produce just enough plutonium to be able to stock one of the eight sub-reactors with MOX fuel. If I wanted to. But I didn't really have a need...
Although it was a fun challenge, next time I'll probably build smaller