I agree you're overstocked-- But it's actually a big misconception some have about rift lake species that they can't be kept with new worlds. Whether you want to do it aesthetically is one thing, but you can absolutely keep many of them together-- I've kept and bred both types for many years. No, having multiple tanks, I don't normally just bunch them all together, but on occasion I've kept some of them together at times for various reasons, including keeping fry either together or divided in the same tank. I've also seen a lot of seemingly crazy combinations, whether in person or because of having been a mod on several forums for years-- stuff like geos and frontosa, even discus and frontosa-- discus is a stretch but I've seen people do it and have it work. Actually, there's a Tanganyikan genus that looks and acts a lot like a geo, so...
Water-- Nearly all cichlids from the 3 major rift lakes will do just fine in pH between 7 and 8 and medium hardness, as will most new world cichlids. I tend to keep my tanks in the mid 7s (pH). There are some exceptions with some black water SA cichlids that tend to be very sensitive and not especially adaptable, but overall most are more adaptable than some people give them credit for. Most species will be fine in temps in the mid-upper 70s to 80-ish, but not all, so temps are more of a question with certain species.
Food-- Assuming a staple of a quality pellet, not much of an issue, not like some think-- with a few possible exceptions, but even some of these exceptions aren't really if you're staple is a quality pellet (or flake). This includes frontosa-- I've kept and bred them for years, Kapampa gibberosa mostly, but also other types.
What it mostly comes down to is compatibility of size and temperament, which is a whole other thing. Of all the possible combinations, some are just fine, some will rarely work or not at all, and others are in between or depend on the individual fish. As for the aesthetics of it, what 'looks' wrong or right is in the eyes of the beholder. Some of the same people who think cichlids from different regions look 'wrong' together think nothing of keeping various gouramis, Asian 'shark' species (bala sharks, black sharks, etc.), loaches, barbs, white clouds, rainbowfish, danios, tetras, and various catfish in their new world tanks that are actually from Asia, Africa, Australia, etc. Again, it's in the eyes of the beholder.
I'm just saying what can be done, not telling you (or anyone else) what to do.