I actually do agree that if its a tall tank, you're better off getting less than the recommeded 3 you could keep in a normal 15G. You might be able to pull off 2, it really depends on personality.
Personally I've had bad luck in keeping puffers together at all ... I've had 3 in a heavily planted 15G ... even though all bought at the same time 1 was slightly bigger ... and within 2 months you could tell. He started acting very dominant and had to be put in a seperate tank because the other 2 couldnt cope with him.
This left me with 1 male and 1 female in a 15G ... this too I had to split up a week ago (After having them for half a year) because he started chasing her badly and it came to the point that she didnt come out of her hiding spot anymore unless we'd chase her out during the water changes.
You just gotta be lucky with puffers ... and I really recommend not keeping more than 2 in your tank, seeing as chances are that your puffers Will start chasing and perhaps even hurting eachother once they mature a bit.
Like said before, sand is the best substrate ... how many inches really is just what you prefer. I've found that the air pockets arent that frequent ... plus they really can just appear at any depth, even when its less than an inch.
Snails like you said is good! However, make sure you're not feeding malasian trumpet snails, their shell is too hard for the puffers teeth and chances are that the teeth will break before the shell will. Besides them, all snails will do. Rule tends to be, snails the size of their eye or smaller ... bigger once will simply get their head bitten off and then be left alone (meaning they rot away in their shell and pollute the water). Smaller ones will be crunched and eaten completely. Bigger ones you can choose to crush with your fingers and then feed to them if you'd wish.
It is however best to feed different food as well. Frozen bloodworms (or live) tend to be the main diet in aquariums with treats of dapnia, brine shrimp, white bloodworms or whatever you wanna try feeding them. Bloodworms however are best
*thinks*
Nope, I think thats all ... nothing more I can think off
*whistles cheerfully because she got to rant and wanders off*
--Edit--
Aha! I remember ... I noticed you said "I'll get 2 females and a male to start" ... dont add puffers after the first batch is settled in already. They'll have their own terretory, plus they havent grown up together ... this WILL cause fights, and most dont stop till death.
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