I have a 90 in a doctors office that has a school of large gold barbs (18-20 or so) A school of neon rosey barbs (another 18 to 20) one gold severum abour 4-6", one temporalis about 4-6" , a jurapari about 4" and about 6 clown loaches. I loose a barb every once in a while, eaten I'm sure. I service the aquarium twice a month performing a water change only one visit per month. It's a pre-drilled all glass with a wet/dry. I think it looks pretty cool, a couple of large main focal points with lots of comotion from the barbs.
I have an opinion to offer about doing an mbuna tank. I have a 150 mnbuna aquarium in a doctors office (pre-drilled with a huge wet / dry) as I'm sure you all know, in order to keep some sort of peace in the aquarium I have intentially overstocked the aquarium. Other wise one dominate fish would slowly kill off his tank mates. It looks very cool!!!! But, back to my opinion.... Because it is so over stocked I'm having to perform major water changes every other week. Now on an aquarium at home this kind of maintenance is no big deal but if some one is going to be paying you to service the aquarium, might want to keep in mind what you will really need to to to keep it right and tell your customer what it's going to cost him. The prices you guys are quoting that you are charging your customers is pretty low, you don't need to be cutting major deal to get the job. Aquarium set up and maintenance is a specialty occupation, charge "em for it.