and I need to know what are the best engines to use to power them. My choices are limited to electrical and Magmatic at the time being.
Magmatic, free, near-infinite energy. Unless you have the abilities to upgrade the electrical engine and you have a decent EU setup.
The engines consume 6EU/t each, so a thermal generator should suffice for four, but the result will only be 8MJ/t. The crucibles want 30MJ/t, each, to operate at full speed.
That you're wanting to run multiple crucibles makes me suspect you're trying to turn netherrack into lava in order to generate power. If so, then you should be using magmatic engines instead of electrical. Don't expect much power back that way either, but at least it should give you a net gain.
If you're trying to convert cobble to lava in order to make power, then, well, don't. Either pump it in from somewhere (eg the Nether) or use bees to generate it for you.
What's wrong with using cobble? It's easy to generate and you don't have to mine it or go to other worlds. I'm starting my world from scratch and because the recipes were changed for a lot of the items, I have to make due with what I have.
Guess I'll have to wait until I make Mystcraft Portals and a Quarry to mine the Nether.