Well, depends how fast you want the mass fabricator to produce UU matter.
I've got a single geo therm powered by a magma crucible and a single normal generator powering the fabricator, no scrap for the bonus. All the power is supplied via a steam boiler and overflow wooden planks from a steves cart tree farm.
Yes, it will be slow to generate UU matter, but I'm not in a rush for it. I think I've got 6 UU matter now, so that's one iridum ore - wohoo!
Since I have sufficient biogas and steam producing MJ, I may upgrade it with a 2nd magma crucible and geotherm generator, or even be a devil, and add 2 more!