How interesting! I just got a 5g hex for my office....and have never kept DPs. Would I be able to have one DP and maybe a snail, a couple of shrimp, and two neons?
puffers are not community fish, they will tear apart those neons and possibly the shrimp (these are hit and misses) and since they are molluscivores they will eat the snail.
I'd avoid Otos unless you have a fully mature tank with lots of diatomaceous algae...zucchini and other blanched veggies in a small tank can quickly affect water quality, so you would need large quantities of algae to satisfy the requirements of Otos.