Welcome to TPT!
A 20-30gal tank would be perfect for a pair of Rams. And if you liked African cichlids, you'll love Rams
. Huge cichlid personalities in tiny colorful packages!
A pair of Kribs also would work.
Plant selection depends largely on your lighting and CO2 setup. If you want a very low maintenance tank, stick with low light/low tech. If you want to be able to keep a wider plant variety, then mid-to-high light and you'll need to use CO2.