For lights, it'll depend on what you plan to keep. If you're looking for something cheap, I'd recommend
these over the ones you were originally thinking of.
I'm planning to use one of these to light my refugium, but I haven't bought one yet, so I can't comment on the quality of these fixtures (yet).
Another thing to watch out for is the Seio 1100 that you're planning to use on the 20gal. This is a pretty strong PH for a 20gal. It's also quite large, so it'll look pretty big in a small tank, however if it's okay with you, then that's all that matters.