I was in a similar situation as you when I started in December. My 215L was from eBay and I thought it was a big tank and can keep most things (at £100 inc cabinet can't really argue!). I was hoping to get a JD or green terror. I started with Sajica, then firemouth. I had a pair of sajicas which were actually fine, until I kept disturbing their cave to clean it, and they had a domestic and separated. They never bothered my other fishes at the time (tiger barbs and rainbowfishes). They only did a bit of chasing when the others got too close. Had to move them on. Then I bought a firemouth, which was initially fine, then when I added a second thinking it was the opposite sex, things turned a bit "nasty". The new (and slightly smaller) one kept being chased away by the first one, to a point where I decide to return both. Now I have 3-spot gouramis as my "centre piece(s)" fish. No fighting. I can even keep shrimps in there.
Mbuna are aggressive. Most cichlids are also quite aggressive, but there are more "peaceful" ones out there. Peacocks are quite nice too. What I would advise you is have a good look around and see what is available in your LFS. Also find a friendly LFS who would be willing to take fish back if things don't work out. One way of doing this is to ask them to recommend a type of cichlids for you. Ask them for advice. That way if things go wrong they would be more willing to take fish back.
Good luck and have fun!
Adrian