Usually, fish of similar shapes will school together, though similar coloration/patterning is also a strong indicator. Even if you had both types though, they shouldn't fight or anything, so the worst it'd be is you would have 2 separate, small schools of hatchets.
There's no reason you can't start planting now, if you'd like to. As the planting gets denser, the fish's territoriality will seemingly go down simply because their line of vision is broken up and it's hard to give a good chase if you can't see the "enemy," haha.
Rasboras and tetras tend to go well with cichlids, in my experience. They're fast enough to get away, smart enough to stay away. Cories are just plain adorable... and a little bit dopey when it comes to learning. Heh.