I think you would want at least an 8'x2.5' tank for a largemouth setup. A tank that size should be able to house 2-4, depending on how big they end up getting.
There are two varieties of largemouth bass, northern and Florida strain. Northerns probably won't get much over 24" (that would be huge) and Floridas might get a few inches longer. Although in the wild Floridas have been known to reach about 25lbs, even one of this size would probably be less than 28"-30". In an aquarium, I wouldn't expect a bass to get over about 20-22" and MAYBE 10lbs.
They will eat a wide variety of live foods, the list basically contains anything that will fit in their mouths (and that can be a suprisingly big object!). They can and should be trained onto a decent pellet food, supplemented by some meaty live and frozen foods such as fish, crayfish, insects, etc.
Room temperature should be fine for either species (65-75*F should be fine). For decor, I would suggest sand, driftwood, rocks, and some live plants. Lily pads would be awesome!
Possible tankmates include smallmouth bass, sunfish, and catfish (channel or bullheads).