It would be a good tank size for dwarf puffers, but in that size (about 12 gallons, the rule is 5G per dwarf puffer, and don't try to strecht it) I wouldn't try keeping more than 2. Even with 2, you'll need it to be heavily planted and you'll need to break up their line eye sight.
Yes , I agree with Erised. However, even with plenty of space, you can't guarantee thatDPs will get on. I tried a trio in a 14g and one DP killed the other two overnight. Personally, I'd keep just one puffer per tank with maybe a BN?