i'm sure theres plenty of people on here who will be able to help better than me, however it might be an idea to decide what kind of puffers you want to keep first and then work from there with respect to designing a setup. Do you want to stick to freshwater, or would you be willing to look at brackish puffers too (ie with some salt in the water)? There are quite a few options for that size of tank, in both FW and brackish, might be worth taking a look at the puffer profiles in the link that Pufferpunk posted recently - http/www.pufferlist.com/