If you have good filtration, some rocks or structure for the fish to use to escape from each other, I believe you could go up to 5 maybe 6 peacocks in a 29 if you get them when they are small and only get males. Yeah, they will get big and you may have to re-home as they grow, but they are an easy fish to keep, very active, and very colorful as they mature. I say no females because males can kill each other fighting for a mate. No females calm them a bit. Not to mention only males have color. As others have said, hybrids can get larger and would not be the best for a small tank. Nor would more aggressive african species.
I've gone the 29 gallon route before with both male and female. Well, after several months, that tank had about 30 2 inch fish. All surviving and appearing happy, but admittedly way too crowded, so had to give some away.
Have a 90 gallon now with I have no clue how many adults. They swim too fast for me to count. They are all healthy and happy. The Orange Blotch Peacock must be 8 inches, but fairly tame. The 6 inch dragon blood had to be moved to isolation in a spare 20 gallon because he would kill every male he could find and mate with every female he could find. Still need to rehome him. I have a 30 gallon sump filtration on that tank which I believe allows me to keep the high population without problems.
Good luck