I see ATO as the most important tool for keeping salinity stable. Smaller the tank more important it is.I agree with everything said above, except that you NEED an ato. I dont think you need it (unless you will be leaving your tank for more than 1-2 days soon). Keep the ato down on the priority list and focus on your lights and test kits. You can forget magnesium and calcium for now since you only have softies. Focus on temp, salinity, NO3, PO4 and alk.