There are various useful puffer resources on the web, including a couple of dedicated puffer forums (which I can't give you links to because of the "house rules" here, so you'll have to Google 'em).
But, in a nutshells, the first thing to bear in mind is that puffers generally need to be kept alone. So you are really talking about buying a single specimen for its own tank. If you can only spare a small aquarium, say 10 gallons, then the dwarf species in the genus Carinotetraodon are attractive. I have two C. irrubesco in 10 gallon tank with some cardinals and baby halfbeaks. C. irrubesco are very shy though and hide most of the time.
Go up to the 20-30 gallon range South American puffers become an option. Unlike other puffers, they do well in groups, though as with all schooling fish, bullying can be a problem, so ideally keep at least 3. They aren't very "charismatic" though, and never really become tame. SAPs would fine with fast moving tetras and suckermouth catfish, but they will fin-nip slow moving things like livebearers and Corydoras.
At 20-30 gallons, some of the predatory puffers like T. palembangensis and T. miurus are viable. They are around 8 to 20 cm long depending on the species. They are sometimes tricky to identify, and differ somewhat in personality. It's well worth reading up on a good pufferfish book, such as the Aqualog one, first.
With bigger tanks, bigger puffers can be considered. T. mbu is widely sold but is not hardy and is intolerant of nitrate (actually, all puffers are, but this species even more so). T. lineatus is another giant puffer. For these, you're after 55 to 100 gallon tanks, at least, depending on the species in question. They also need a decent filter.
There are various threads here and in the brackish section on feeding. Puffers will usually eat anything meaty (including tankmates), the question is what's best for them. Snails and unshelled prawns are the ideal, but many species have a marked preferance for bloodworms. Krill, brine shrimp, small pieces of squid and fish, mussels, cockles, even frozen peas are all suitable foods. Live foods will also be accepted. The small species like daphnia and brine shrimp, while larger ones enjoy river shrimp, crayfish, and of course snails.
Cheers,
Neale