setting up a small tank for a puffer please help

Most of the Dwarf Puffers I can think of are actually fish which prefer a proportion of salt in the water to make it equate to 'Brackish' conditions as they are estuarial fish in nature. I have kept them in completely fresh water on many occasions but they do seem to do better in slightly salty conditions.
This makes plant selection a little more difficult if you go down this route.
Some of the Pygmy Puffers come from entirely Fresh Water and would be more beneficial in many ways, including the lack of a need for any Salt.
These have been discussed several times before on the Forum, try entering Pygmy Puffer into the "Search Forum" facility top right), you should locate the postings there.
Personally I find these to be quite engaging little fish but mine will not eat any prepared foods - although they will occasionally have a nibble at frozen Bloodworms and Brine Shrimps they really seem happiest when eating freshwater snails. They find it hard to 'chew' into the shells of the so-called 'Trumpet' snails although I have witnessed them attacking the meat of the snail when it appears from the shell to move.
They are quite nippy - especially with 'prey' which are slow-moving so perhaps you would find lumps missing from the Otocinclus you plan to have in the tank. My advice would be to just have four or five Pygmy Puffers - you'll find them entertaining enough on their own (just as long as you can provide enough snails for them).

John

These Pygmy Puffers only grow to around 1" total length.

There is quite a lot of 'posturing' that goes on between them but if the tank is fairly well planted with bits and pieces of cover for retreats you should be fine with four (or five at a pinch) - but you really would need to get the tank set up and well established before adding the fish.

John