couldn't I just do like 1-3 haps and then like 20 peacocks?
The biggest problem with them is not going to be the number of haps but the size and attitude as compared to the peacocks. Your average peacock is going to be 5" and pretty laid back and mellow. Your average hap is going to be around 8"-10" with some like the Dimidiochromis compressiceps or venustus which you mentioned getting to 12" and being a bit aggressive.
Not saying it "can't work" but just letting you know there will be a good chance of some issues with the haps stressing the peacocks.