Ditto the above comments:
Do not trust the sales sites to tell you the right info. All they are after is your money.
1. I had several compatibility charts from various sources Thatfishplace, Petco, Liveaquaria( which are run by multiple doctors(vets), etc... They all show the fish is fine with what I had
These places are all in business to get money. They will say whatever they need to so you will buy.
Seriously Fish (linked above) is a much better site to research the fish.
Also, asking on a forum, and researching on a forum. This will get you a range of answers.
When 'the votes are in' go with the worst case scenario.
Housing matters, both the size and shape of the tank and decor, as well as the tank mates.
A very rough guide:
Most fish are going to be more aggressive in a smaller tank.
A tank with plants, wood, stone and other things appropriate to the species can calm them down. Territorial fish will focus on protecting their territory, and not try to claim the whole tank when they have a cave or whatever they need in a larger tank.
My experiences with the fish listed so far:
Serpae Tetras: are much more aggressive than Red Phantoms, Peppermint Tetras or other similar fish. Check several references and go with the milder one if you are looking for a red-orange fish. Similarly, whatever fish you think you want, there are probably others with a similar look but different personalities, or water requirements so you can probably find something that will give you the look you want but is more compatible with the rest of the tank.
BA Tetras: I have only had one, a contaminant. He was in a 4' long tank with some other rather pushy fish, so was not a problem. I had read they could nip plants, so I did not go get more of them.
Bettas: I have had one Betta that was very shy in a community tank. I moved him to a smaller tank where he was the only fish and he was much happier. I have had others that did fine in a community. But I did not keep nippy or pushy fish with them. They were the only upper level fish. Tank mates were lower swimming, including bottom fish.
Gouramis and Anabantoids in general: Most are territorial and can be anywhere from semi-aggressive to killers. Yes, some species are more aggressive than others, with Dwarf, 3-spot, Paradise Fish and Betta splendens topping the list. Another problem with Dwarf Gouramis is Iridovirus. Choose another fish.
Lumping all Tetras together- I guess they do not carry the Bucktooth Tetra. (Exodon paradoxus) (no, I have not kept this one)
Panda Garra: I am looking forward to getting some. I understand that several will keep the arguments between each other, and they won't bother the other fish so much.
Garra flavatra ? Panda Garra ? Seriously Fish
Flagfish: I have had the males argue about territory, but only with each other. I have not seen them bothering the other fish.