I've had a planted tank set up for a few years now. I often have just fish and some java moss in it because I become lax with caring properly for the plants, lol. You could use something like laterite under gravel (make sure it's small size gravel for when you decide to go with plants). If you plan to use the same tank for plants later just make sure it's a fairly fine grain rock if you go this route. You could also go with Flourite or the EcoComplete. Just cycle the tank like regular adding fish slowly. I use a Marineland Emperor 400 on a 50 gallon and don't have much problems with plants when I'm really working with the tank.