Cichlids will pick at your plants a little or destroy them or leave them alone, they have personalities, personal prefrences and are very fish by fish.... I have plants in my tanks and the plants are all in tact at the moment. They do destroy the moss balls tho. Plecos eat the heck out of the moss balls too. I buy them from a lady who sells them for a buck so eh... not a big deal to me.
55 gallons with that type of water hardness (7.8-8) spells cichlid to me too!!!!! Fishman hit it right on the head. I have a good post with stocking tips on the cichlid forum under "getting back into the hobby" with how I would stock a new 55g.
Basically tho.... I would go to the LFS and buy 15-20 pretty mumba and a pleco or two. Honestly people will tell you this or that about stocking combos but REALLY there is no wrong or right way to start an african tank. You will get some jerks, some whimps and some in the middle. I would avoid buying too many of any one species and if you can select more females then males you will have a little less aggression.
you could get away with a south american tank on those paramaters too it woudl just be far fewer fish, and yeah with SA/CA fish you basically need to use aquarium silicone like glue to glue your decor to the floor. They will still rip it out. They are fun and tend to have big personalities to go with their equally large size.
DONT buy africans and south americans at the same time. the SA/CA will get huge, they fight differently, and they have different nutritional needs. I read soooo many posts here where someone got a convict, a jack dempsy and some various mumba. Well it always ends up in disaster.
So yeah you could get away with as many as 25 in a 55 (maybe push it to 30 total if you start with small fish) ** begin crucifiction for suggesting an initial overstock given new fish will be juviniles and many will not make it**
Here is my thing about cichlids and stocking, they grow relatively slow, they are actually less aggressive when heavily stocked, and to be honest a year from now if you have half of your initial stock I will be impressed (with ANYTHING you purchase, not just cichlids) So yeah cichlids are really cool, you will get to really liking them i promise its not by accident that big fish stores have soooo many tanks dedicated to such a specialized fish group, it's because cichlid people get into them and just can't stop
I would start with juviniles and grow them up, it won't help them get along better but it is pretty fun to watch a 1" fish turn into a 4" fish