Hi, 10 or 15 Trichopsis vittata would be fine in a tank that size, when rivals display to each other there's space for the weaker fish to withdraw so it doesn't develop into an actual fight. Also females who are not ready to spawn can get away from any unwanted attention.
The aggression is only between rivals, they leave other species alone, but their long fins are very tempting to any tankmates with fin-nipping tendencies.
I've kept them with small, peaceful fish like Harlequins, Chain Loach, Five-banded Barbs etc.
They are lovely fish, but don't always show their best in a dealers tank. As long as they look healthy they will develop their colours after settling into a well-planted tank.
I haven't had any for a while now, the more I think about them, the more I want to get some again,
I might have to go looking after Christmas.