They had one in spring and one at the start of September. 10, 20L, 29, 40B, 55.
I think a puffer would need more space and make sure it is truly freshwater. A lot of them are either salt to start or fresh then salt as they age.
Shrimp, 2-3 male Guppies, all females. But if you do get one male and 2 females, don't keep fry unless you plan on taking out another fish.
But yea, Walmart has 10 gallons for only $13, you should get one of those and transfer all your gravel, filters, heaters, plants, etc over.