I have a 20g with 9 rummynose, 6 neons, 1 honey gourami, 1 GBR, and some snails and ghost shrimp. You could easy do a pair of rams though.
I respectfully disagree on needing a sterilizer too. While useful it is largely unnecessary -- just make sure your tank is at least a few months mature and all of your levels are stable. A hardier option to GBR is the Bolivian ram, which gets just a tad bit bigger and are noticeably less colorful. I'd honestly just go with the GBR though, just make sure you're getting healthy and preferably local-bred stock. Good luck!
Edit: Just wanted to note that your current is fine. If anything you'll want to upgrade your filters at some point, possibly looking at something like dual Aquaclear 20s or an Aquaclear 50.