I like the change in strategy. Bill is right in that you will have some trouble identifying different females, so you have to be careful.
From your list below, here's what I'm thinking you can and can't get away with.
-Placidochromis may be tough. I have only grown out and spawned P. electra and phenochilus and they are somewhat similar (blue with black vertical bars). If you got the fry separately, you may be able to tell, but I can't recall differences off the top of my head. Not sure what the other juvenile Placidochromis patterns look like, but probably very similar.
-Copadichromis - Gonna be pretty rough to tell I think. There are some very obviously different female melanin patterns (mloto "Fluorescent" has no spots, borleyi has dark fins, but you are not getting either of these). I haven't kept virginalis or trewavasae, but believe that they're both silver fish with 1-2 spots.
-Otopharynx tetrastigma - pretty sure they will be ok. I've tried to go back and look for old pics of them when I had them a couple years back. Could only find shots of the boy, but I believe that the females have no melanin. Could be similar to the lethrinops, but the head shape would be the giveaway (lethrinops have sort of a snub nose).
-Otopharynx lithobates - no problem. Elongated body, 3 spots, they all turn brownish/camo at about 1.5"-2".
-Mylochromis/Cyrtocara moori/Protomelas - All very distinct from the rest.
-Aulonocara will be tough. If you tried two groups together, the red jakes and something else would probably work. The red jakes (Otter Point and Eureka) females are straight up brown and have orange trim on their fins whereas most other peacock females are sort of silver. S. fryeri look a bit similar, but are more elongated and do not have the vertical stripes.
Again, when I say that something's ok, I mean that they will be ok to grow out together, but some will have to be separated once they mature or they will fight and/or interbreed.
I'm partial to this method, because that's what I did. I'd say 90% of my breeding groups were grown out from 2" or less - most smaller. It's a great way to do it, but unless you're careful and judicious with getting rid of fish, you'll end up with 15 tanks before you know it, lol.
If you wanted to stick with all males,* then get 5 very different looking groups to grow out. Get 6 of each. Grow them out. Trade off extra males/females for ones you don't already have. This would be a very economical way to do it.
*If you decide to instead go with a number of groups in the tank (similar to my 180), then you're already there. I'll get into which groups would go together long term when I get some more time. Alternatively, you could always setup a 40 breeder or 55 to keep a group you really like.
Anyways, I'm rambling and need to get work done. If you have time, come over and check out my fish room. You're always welcome.
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