dwarf puffer tank only need to be 5 gallon for a single specimen. 3 more gallon for each dwarf added.
The tank would need to have some sort of plants (live or fake) to break the line of vision for the puffers to reduce aggression.
FW puffers are quite (or very) hard to come by so you may want to look for something else. Not sure what other fish would have a personality like a dp