They go through a lot of snails. I started with three puffers and ended up with one; I strongly suspect they didn't get enough food, despite my best efforts, as they always looked slightly hollow bellied. I lost two very quickly (within a couple of weeks) the other one I had for about a year, and he ate four or five snails (about 5mm shell sized) every day.
I, at first, did what you're planning; but I very rapidly realised I would have to start breeding snails; I would very, very strongly advise you not to try keeping pea puffers unless you've got a good breeding population of snails. If they don't take to frozen foods, you will need the snails, no doubt about it, IMHO.
You don't need a lot of room to breed common pond or ramshorns snails (my puffers couldn't get into Malaysian trumpet snails; they have a very hard shell, even as newborns); any sort of container will do, and it doesn't need filtering or lighting; just daylight and some plants. I used little goldfish bowls quite successfully (I still have them going, even though I no longer have the puffers!)