Welcome! I just started a new 20g tank and I would highly recommend live rock and live sand as well as AquaClear HoB filters. I've got three AquaClear's and just ordered a fourth and have never had problems with any of them. Macroalgae is definitely the way to go and will make maintenance easier and the tank much more stable, they act much like a skimmer. I also have a UV sterilizer and I don't recommend them unless you're having a real algae problem (ps: they won't hurt macroalgae). An ATO is also a great investment to keep maintenance down, however I find that a tight lid on small aquariums prevents most evaporation (I only top my tank off ~once a week). As far as livestock goes, I'd be weary of adding anything other than a very easy fish at first. While not the most colorful, tailspot blennies or some small gobies make a great first fish. You could also try any kind of firefish: they are very colorful and stay relatively small, plus are cheap and easy to find. Note on the gobies: some are not easy to keep, especially the "sand sifters", so do your research. While a lot of the information you'll get is subjective, I can objectively tell you that you've come to the right place. Everyone here at R2R will be glad to help you and will lend years of experience. Always feel free to ask any question you might have, that's why we are here! Good luck with your tank and welcome to the hobby :)
