No you're not insane, that Big Reactor looks just like mine!
arent big reactors fixed to sizes like 5x5x5 9x9x9 etc? also you are crazy as soon as you actually fill everything with liquid cryothium or liquid ender ^^
I think they can be as big as 32x32x48 or something ridiculous. I used to build mine small and tall... until I did some research and learned that it is much better to get as many fuel cells on one level... and thus my 15x15x5 reactor. If I could have made it 32x32x3 that prob would have been even better but I wanted to keep it in one chunk, so I kept it 15 blocks square. I can always extend it vertically if I need more power. I have the outer block as liquid ender and then 2 blocks of cryotheum which leaves a 7x7 area for my fuel cells and I checkerboarded them with cryotheum in between.
As long as you have enough redstone, the cryotheum is pretty trivial. Snowballs are free because water is free. All it take is spending the time to make enough and place it down one bucket at a time. Took a while, but well worth it. I get about 45,000 RF/t at peak output. Wow, I see the fuel usage just went thru the roof in 1.0.2, I loaded up my game to check my figures... ouch, that's brutal, at peak power it says I'm burning up 4 mb/t, which is 80 mb/sec so approx every 12 seconds it uses up one Yellorium ingot. That's ridiculous, but I pretty much stopped playing the modpack and went back to GregTech, so meh. LOL