Do a bit of research, best start is looking at independent shops, see what they're looking for. Next is look at local clubs, see what's selling & who's breeding what. Being near the Twin Cities you've got MAS; Announcements - Minnesota Aquarium Society
as well as the forum associated with their club; Minnesota Fish Keepers Forum • Index page
Depending on what you plan to breed & sell you might get by with a couple tanks with livebearers, up to several if you want to try larger cichlids or offer more varieties of a species. I do angels on & off, so it's a couple dozen tanks, maybe close to 35 when I'm really rolling.
Shipping can be a pain, I'd rather pop for a tank of gas & drive for a few hours to an auction or swap, sell 100-200 fish, dry goods, blackworms, whatever. It gives you an opportunity to see first hand what sells & why, and what doesn't. You can also come across some awesome deals, makes for setting up & running a breeding operation much cheaper.