Hello GodricPuffer, guess what, tommorow I'm buying a 20 gallon and the substrate/equipment for a pair of baby GSP's so I can start cycleing the tank (they are tiny I'll upgrade when they are bigger). So we are in the same boat! I know what it feels like, you want to make sure everything goes as smoothly as possible. From the research I've done I'd say yes to sand, If you want to plant it look at the thread below that says "Puffer Plants". For a Filter I'm not to sure, the external canister's seem like a good idea and there are many ideal for up to 30gallons which should be the right size. Let's keep each other updated on the progress.