Yeah, I'm definitely jealous of you! I have a 75 right now, plan on moving up the ladder in due time.
For a 55 gallon people say the max fish count is 20. So I'd assume since your tank is double the footprint you could do 40. But you can fudge the numbers with demasoni and rusty as they are both dwarf mbuna. But a healthy, properly stocked tank I could see: 12 dem, 10 rusty, 10 lab, and 8 acei.
Of course you want to buy more than that in the beginning to fix your m/f ratios and to make the tank look fuller as they grow out. Just make sure you go through an LFS that will trade with you for not only other fish but for supplies.