Everyones pretty much covered all the important stuff, the website Dwarf Puffers : Home
has a lot of information about these little guys.
Dwarf puffers will get more agressive as they become sexually mature. The will usually kill off other tank inhabitants at this time. You want 1 male to 2 female ratio, but they are really hard to sex as juveniles.
Most dwarf puffers will do well stocked with oto cats, aprox 95%, and 50% can be stocked with ghost shrimp, the other 50% of the time the shrimp end up as food.
I've been researching and building a dwarf puffer habitat for a few months, I hope to get my own tank up and running in the next few weeks.
Test kit: You want to use a liquid test kit. Most experianced aquarists recommend the API freshwater master kit. You should be able to find one at all three stores you listed, and I've heard the walmart online store sells the test kit for about 20$.
And for using the raw shrimp method to cycle your tank, use raw
shrimp, not cooked. Most large grocery stores should have raw shrimp.
Good luck with your endeavor, I'm tagging along