im looking into the same thing myself. There messy fish so even though you can fit 3-4 in a cycled tank they probably wouldn't do so well since they poop so much. But also at the same time since they are aggressive fish they also may not get along with each other. I am thinking about maybe 1 puffer and a oto to balance things out but im not sure if they both fit.
Also doing some research has showed that they use a sand base since they like to bury themselves in it. Also you will need to look into snails as a source of food every few days to keep there teeth from growing to large.
If you say so. I have mine, and I know their size and behavior. There's just no way a shoal be able to do any of the things they do when they're happy in that size tank. They may well have survived, but what kind of activity did you actually see in them?
4 gallons isn't enough for tetras, they need to be in groups and are active swimmers.
According to the very good profile on this site on dwarf puffers, you should be able to have 1 dwarf puffer provided keep on top of tank maintinance. http/www.fishforums.net/index.php?showtopic=136616