Live rock isn't as "nessisary" as everyone claims, they tend to recomend up to 2lb per gallon, but I believe thats just propaganda created by the companies that sell live rock, as I have seen many tanks do well with significantly less. You could easily get away with 0.5lb per gallon, and If you want you could get only a few lbs of live rock and get base rock for the rest (base being cheaper, but becoming live with a little time). Sand you will want at least 1lb but up to 2bl per gallon, of a fine grain sand, sugar or select grade, crushed coral is bad so avoid it, how much sand you want depends on how deep you want the sand bed.
Stocking, since you don't want corals at the moment any lighting will do, as its more or less completely astetic. Stocking a 75 you have alot more options then the average tank as it is larger therefore more fish can be in it. Since you want corals you will need "reef safe" fish, but that could mean predators or community fish, as there are "reef safe" fish in both catagories. Though you have more options with community fish then predators.