Overpopulated - yes, broadly but perhaps more so with mbuna than others. You overstock to manage territorial aggression. Basically there will be too many fish to allow any one or two fish become hyper dominant and attempt to claim the tank as a territory.
You will want to consider whether you prefer Haplochromes ('haps', Peacocks (aulonocara species) or mbuna.
You will need a reasonable size tank (a 55 is good for peacocks or mbuna) and seriously over filtered to cope with the stock levels.
Check out the links given to you above for some good info, profiles etc.
Personality wise, broadly speaking they all have a ton of personality, but interact best in groups and not as single specimens. Equally, sometimes their wonderful personality manifests itself as sociopath-murderer. Certain species are best avoided particularly when starting out.
If you go for mbuna you could look at :
Pseudotropheus Socolofi - nice albino version of these too.
Labidochromis caereulus
Labidochromis Hongi
Iodotropheus Sperengae
Psuedotropheus Acei (either variety)
Pseudotropheus Lombardoi
Cynotilapia Afra
Those are some good starter mbuna as they are considered relatively less aggressive.
Ideally you stock 1 male to 3 or 4 females in each group and I guess in a well filterered 55 Gallon you might consider about 16 or so fish in total to start - they will breed in a puddle during an earthquake presuming good clean water so you will likely end up with fry growing out in there as well.
They're great fish - read up on them, get the right set-up and you won't regret it.
