Hey Justin.
Stocking tends to be a tricky subject with this species (and many others. but we'll stick to exodons to answer your questions). Traditionally, most people will suggest to stick to the 1"[2]//G rule. This is a good starting point, and will help you maintain your water parameters without all the additional maintenance. so conservatively, at an average of 3-3.5" max, youre looking at 8-10 exodons in your tank. which is the minimum i would suggest keeping as a group.
Now... with that said.
With proper filtration and maintenance, you can definitely keep more than that. but the amount will be determined by the amount of work youre willing to put into it.
With your current filter (the
Eheim 2213), youre getting around 4x turnover (before factoring in the pump head). While many people will tell you that 4x turnover is fine for a properly stocked tank, for me, its barely sufficient. But i likes me some filtration. hahah. Luckily though, the
Eheim 2213 will give you excellent bio filtration.
As others have suggested, i would highly recommend an AquaClear HOB in addition to your canister. IME, they are by far the best HOB on the market, and i cant recommend them enough. Higher turnover, Additional WC, and proper cleaning will "allow" you to up your stock a bit, without any negative effects, but it will require more work. So just keep that in mind when determining your stock.
and as mentioned, they are known to kill their tankmates, even when their tankmakes are their own kind. so keep them well fed. (i do 2 small feedings a day rather than one large one).
for those who think they only eat scales.
this guy got picked to the bone by his friends.
also, for the record, the user in question, "attempted" to do something that has been done on and off this forum numerous times, and was unsuccessful. inductive reasoning will conclude that user error is the reason for failure. however, in classic immature fashion, he would somehow imagine that the cause was poor information. some people just have a hard time getting things through their heads.