Actually limestone buffers your Ph to be higher so it is recommended for Africian cichlid tanks. Also, plates in a cichlid tank can work out fine, you just have to know what kind of plants that are good for the tank. Check out cichlid-forums.com
If I were you I'd go with sand instead of gravel as your substrate. Cichlids really like sand as they like to play in it. It makes the tank look 100% IMO as well. I will be switching my substrate to PF sand once it get a little warmer outside. If you are interested, I'm looking to get rid of a few fish. Most of them are about 2.5-3 inches, and I've be very flexible on price. I have 3 Red Zebra's, 2 Bubblebee's (Ps. Crabro), 1 Ps. Acei, and 1 Melanochromis auratus I'd like to find homes for. This is a very good community so far, haven't had a problem or a death since I started the tank about 6 months ago(you really shouldn't mix different species of the same genus, but they have been getting along fine).
I'd also recommend that you get a larger filter, be it a HOB or canister(I perfer) just b/c the amount of bioload that cichlids put out. I'm currently running a Fluval 405 and an AC110 on my 75G africian cichlid tank.