Good for you, for doing your reseach!! It is a big decision and there are a ton of cichlids out there that you can pick from. Plastic plants are great, they look better than live ones in my opinion, and many cichlids will eat live plants, but they will only dig up plastic ones!! Which you can just easily push back down into the gravel.
There are two books that are really great, one is called "Enjoying Cichlids" by Ad Konings, and the other is The Cichlid Aquarium by Paul V. Loiselle. Both of these books will give you an overview of all cichlids, and then you can decide what will work best for you.
I think it is best to do a Biotope type tank, where you pick a certain species and then build your tank around that. You pick cichlids that are also found with your Target fish, and maybe even find some non cichlids that might work. These types of tanks do really well, because the fish have the same dietary and water requirements, and will be easier to take care of in the long run.
Your tank size is going to be marginal for Malawi Cichlids, but if you pick the right tank mates it should be okay. As far as Central America goes, the fish are generally much larger, and you are more likely to end up with just one big fish! Doing a South American tank their may be a little more variety available, and easier to do some other non cichlid species.
So don't let all the different kinds of cichlids overwhelm you!! Do some research, and see which cichlids are catching your eye, and then you can narrow down your picks, and concentrate on a few species. I am better at telling you why your picks will or will not work, then telling you what you should keep.
Hope that helps!