I've posted so much about angelfish of late that I can't remember where I wrote what. So at the risk of repeating...
Angelfish is a shoaling species so there must be five minimum or preferably more, and that means a tank of 4-feet (a 90g is really about minimum) or larger. Once the angelfish are together in the tank, a fairly good hierarchy will quickly develop. This is one reason why additional fish cannot be added to a group that has been together for even a few weeks. There are no guarantees as individual fish can deviate from the normal, so when setting up a shoal of angelfish there should always be a back-up plan just in case. Also, one or more pairs will likely form within any group, and if the tank is not sufficient space this may mean moving either the pair elsewhere, or the other angelfish elsewhere. And there could obviously be one, two, or more pairings depending upon the group size. Again, a back-up plan is needed.
The only other humane way to keep this fish if not in a proper shoal is as a bonded pair if one forms. One solitary fish is sometimes seen, and while I cannot say how the fish might feel about this abnormal environment being forced upon it, I don't consider it advisable.
The species is mildly aggressive generally. Males are territorial, but within a good sized shoal this plays out usually without incident. But it may not. I have frequently posted an illustrative video of a group of 11 wild
Peterophylum scalare in a 750 liter (200 gallons) tank with dimensions 200cm x 65cm x 65cm (78 by 25 by 25 inches). Down in the comments the owner mentions this tank not really being sufficient and intending to move them to a larger. But the interaction between the fish in this video is
exactly what can be observed in the habitat, and this is how this fish should be housed.
Tankmates are possible, if carefully chosen.
Corydoras obviously can work (
C. duplicareus in the video as this species manages with the warmth wild caught angelfish must have, commercially-raised fish are different), upper level shoaling fish like some of the medium sized peaceful characins (never linear fish, the disk-shaped species like the Rosy Tetra clade work well). In
very large tanks, the Black Ghost Knifefish in a group makes an excellent tankmate. Both fish prefer dim light, another feature of good husbandry of angelfish.
Spawning is another topic and easily found online. I'll just note that a pair may spawn a few times, but if they have not accepted each other and actually bonded, one will be dead before long. Bonded pairs have been known to live together for years. But divorce cannot be ruled out.