Well, a lot of that information really depends on the species of fish. Typically, I find that most Africans prefer sand substrate (its natural for them, after all) - and it is definitely not as big of a pain to keep clean as some people might tell you
In my opinion, the best filters out there are AquaClears, and on a 55gal I'd either do two AC 70's or one AC 110 (what can I say, I like to overfilter). Lighting, from experience, usually shows off the colours of your fish better if it is a blue-tinted fluorescent bulb (I use AquaGlo bulbs by Hagen, dunno if you can get them down there?)
Live plants won't really work if you're going to be stocking a mbuna tank, but you could put some hardier types in with haps/peacocks, and maybe Tangs. How to decorate the tank, again, will depend on which type of fish you're putting in there.
Also, how many fish you can put into your tank GREATLY depends on exactly the species involved. If you have a look through the profiles at cichlidforum.com, you can get an idea of what fish you like, and build up a stock list from there (with help, of course!
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Anyway, just remember to ask as many questions as you need to, and do your research before actually stocking the tank. Cichlids are awesome fish, you'll be hooked in no time!