Welcome aboard. I was in a similar spot a couple of weeks ago when setting up my 23 gallon. I wanted to go with a smaller tank to see if I liked it and to get practice with water parameters. Go ahead and set it up with the water and sand. Drop a shrimp or 2 in there and put a power head in there for movement. If you plan on a fish only setup it wont cost too much. Be prepared for about a 3 week wait, sometimes longer. Monitor ammonia, nitrite, and nitrate. First the ammonia will spike and then drop as nitrites increase. Ammonia and nitrites must be at zero and maintaining for you to safely add a fish.