I would like
Electric yellow lab
Red Zebra
Sunshine Peacock
Msobo or johanni
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Some nice choices. Your main issue would likely be whether the Peacocks will be OK with the Mbuna (all the other fish you're listing). The Peacocks like more open swim space, the Mbuna like rockwork (they have a way more flexible spine to allow them get in and out of nooks and crannies) and also most mbuna are more aggressive than most peacocks, which can mean the peacocks suffer at feeding time or in some tanks are simply killed.
However, I personally found the Sunshine Peacock strain extremely aggressive as far as Aulonocara/Peacocks go; probably a result of the intensive breeding for bright colour, so this choice has a chance of working out.
So in the 75 you should be ok as long as you allow for some swim space, together with serious piles of rock.
That said, I'd be inclined to consider not taking on the Red Zebras together with the Johanni/Msobo simply because they are amongst the more aggressive mbuna and can be a handful if you've not kept Malawi's before - but if you're comfortable with the idea then by all means go ahead.
If however you'd prefer a fish with generally slightly less agresssion, for blue colour consider pseudotropheus socolofi. If you like very dark blue/purple shades consider pseudotropheus acei. For something a little different but very attractive consider iodotropheus sperengae (rusty cichlid).
All the fish we're talking about should be stocked as either 1 male specimen only together with other males of different species and colouration (you would do this as a necessity in a smaller tank than is available to you), or as groups with a ratio of 1 male specimen together with say 3 or 4 females; stocking with less females makes it likely that the female will be harassed excessively, stocking with more males than that ratio means the males will likely have issues with each other.
The labs and rusties are a little more gentle than other mbuna and would prefer to be in slightly larger groups than some of the other nut jobs, when stocked with these more aggressive fish.
Say you got the 75; I'd go for something like :
- 6 labs (1 male, 5 females)
- 6 rusties (1 male, 5 females)
- 4 johanni (1 male, 3 females)
- 4 Sunshine Peacocks (1 male 3 females)
- 4 Pseuodtropheus Socolofi (Albino) - personal favourite of mine; beautiful pearly sheen.
If you do that you should have pretty much no hybridisation, but you're a bit tight on space for the fry (and you will almost certainly have fry), and it can be fun to raise up your own fish. If you fancy having more room in this regard, lose one of the groups of fish.
Your other option on the Peacocks, is to go for 3 or 4 Male specimens of different species avoiding any similar colourations whatsoever. They'll all probably have a go at each other but 4 of them together with the Mbuna should spread each other out sufficiently to prevent murder. I would personally try this if I was setting up a 75 of mixed malawi - great flash of colour for your tank.
All that is very ball park stuff - there are no rigid rules in stocking Malawis, but there are guidelines which you ignore at your peril (the male/female ratio in particular, stocking seriously aggressive fish with each other etc.).
One other piece of advice; when starting with this fish establish what policy on returns your LFS has; occasionally you just get a fish with that bit more 'personality' than you'd like (i.e. murderous intent) which simply will not slot into your tank - you must have plan B ready to deal with these fish which means either another tank (woot!) or return to LFS.
