I love my big community tank, and the vast majority are groups of 6 or more Tetras of various colors and sizes: Tiny little green neons to 3.5-4" emperors. I like them because they are easy to keep and colorful and active.
But I also have a school of 6 or 7 pepper Cories, several colonies of dwarf cichlids, ADF, C. apple snails,sparkling and honey gouramis, three types of loaches/botia, a short finned Betta (Waldo), 1 Beckfordi pencil fish. (I have tried three times to keep a school of them, but they are a bit hard to keep apparently), and scarlet badis badis. I think that's it--Oh! a couple of pigmy cories--survivors. All these share a 100 usg. I would love to increase the community to 180 usg. So many delightful and interesting fish and so little room.
I have a school of harlequin and pork chop rasaboras, but I can't put them in for now. The tank is stocked for the moment. So the rasaboras are sharing with the emerald Cories (not true Cories.)
A seven gallon would be good for a school of Cories, who are incredibly hardy, and some are easy to breed, and full of personality.
Other than them a good starter fish is a school of small Tetras. They are a good starter community fish, I think.
Mind you they are not my favorite fish; I love them all. But they are a good base stock.