I would buy mostly base rock, or dead rock and seed it with maybe 10lbs of live rock from your LFS
, alot cheaper to do that way and the dead rock will become live after a few weeks and then a few months later you won't be able to tell the difference.
You can fit a good amount of fish in there, kinda up to you as to what kind of tank you want. Will you ever e going to corals? If so there are some fish that arent reef safe.
Heres an excellent site Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums
You can see what fish you like and it will tell you how big of a tank you need, what the fish eats etc...
And yep, you can have inverts including shrimp, as long as the fish you pick don't eat them. Some fish will eat inverts. :-O