You could get a few hardy saltwater fish first. Get about 50# of live rock for the biological filter and either go bare bottom (no substrate) or fine aragonite sand. You can always get a PC light fixture later on and add a few hardy soft corals or LPS corals

Just make sure you get a skimmer and/or do frequent water changes. The skimmer/water changes help to keep the nitrAtes low (keep them less than 10 ppm). Whatever you do, either get a ro/di water filter system or buy it from a LFS to reduce algae outbreaks.