I agree with cd on questions 1,2,3. but I just wanted to add a little to number four. IMO the shrimp will have a better chance, but it is liable to eventually become lunch. Now if you add a huge shrimp or something now, let it stay there for 6 months or so, then add a very small fish that you expect to eat it, then the fish will grow up looking at the shrimp lke its bigger, (this is only true for most fish). Overall if you add the shrimp(or whatever it is) now and then add the fish later, your shrimp will have a better chance of making it for at least a longer period of time. If I were you instead of adding the shrimp then fish, I would add like a clown or something similar, just to make sure that water params are all correct. Then your clown will not pick at your shrimp, and you will have a cool little fish to look at. unless you got a maroon clown or something.......what kind of fish and shrimp or invertebrate are w talking about here? just out of curiosity.