A 5gal doesnt offer enough space for a species like tetras to shoal in properly, they wouldn't really be happy in it so i ould opt for 0.
On the other hand there are other fish that can go in a 5gal and be happy, like a single dwarf puffer or male betta, a small group of pygmy corys or oto's or a herd of ghost shrimp- you could also have apple and giant ramshorn snails along with the fish, they are quite attractive, but only a max of 5 as they grow quite large and produce as much waste as any other 2inch fish out there.