1. Tilapia, perch, and catfish are popular. I have catfish in mine. You just have to match the temperature requirements to your climate/area. 2. You would get

1. Tilapia, perch, and catfish are popular. I have catfish in mine. You just have to match the temperature requirements to your climate/area. 2. You would get the fish at a fish hatchery, there should be one near you. This is something I find out for my customers. You can also buy fish online, but the overnight shipping makes it a bit expensive. 3. You can buy fish food online, or at a hatchery, or e.g. Tractor Supply. 4. The thing about different fish species (or even same species but substantially different sizes) is that if a fish fits inside a bigger fish's mouth, that bigger fish will try to eat it, unless the smaller fish has somewhere to hide, like aquatic vegetation. This is something I will be experimenting with more.