Tugwell: as a guy who's worked in architecture and building since 1963, I've seen a lot of slabs, and learned a bit. You've gotten a lot of good advice, and I'd second the use of steel wire, a 4" slab with 3500# mix, and some sand or pea gravel over a 6 mil poly vapor barrier. I didn't notice where you are, but if it's a colder environment, some air entrainment is good where the slab might be subject to freeze/thaw. And, for that matter, some rigid foam insulation around the perimeter is great, if you'll be heating the space above. You want control joints (for the shrinkage) no more than every 20' or so, all directions. I have used epoxy finish on new slabs, and can't recommend it too highly.