Most canisters will be pretty expensive - but for that size the price is worth it. I like the marineland ones - marineland magniflow 220 would be good for that size tank. They aren’t super good at aerating the tank, so it wouldn’t hurt to add an airstone or powerhead to help add surface agitation.
For stocking, if they liked the ram idea, rainbow cichlids, blue acara, OR convicts are an option along with dithers and a bottom feeder like a bristlenose pleco. They are all attractive, thrive in your natural water, and are pretty easy to keep.