Puffers are easy. You don't have to worry about anything special with them. Keep up water changes (they can be messy), maybe supply a clam still in half of it's shell occasionally and you don't have to worry. They have teeth that continuously grow and form a beak like shape. The teeth can outgrow the puffers mouth and prevent the fish from opening his mouth wide enough to eat, that's what the clam is for. As he picks at the flesh, he will wear his teeth down on the shell. A lot of tobies (dwarf puffers. Valentinis, blue spots etc.) will grind their teeth away on the rocks in their own time, so the clam may not be necessary.
I've only owned tobies and toadfish, so other puffer species may be more difficult.
As for boxfish and cowfish, they can release a deadly toxin when they die (usually only if the cause of death is stress related) which can crash a tank very quickly. The way around this is to either keep them in a species only tank, or build and stock the tank around the actual fish. There is a thread on here somewhere about how to deal with cucumber toxins when released into a tank, I'd give that a read as the way to remove cowfish toxins is the same.