7.2 cu. ft. will get you about 4 5-gallon cornelius kegs by the looks of it. Homebrew Talk has a well-documented topic about someone converting that freezer, and it looks as though he's strapped his CO2 tank to the outside. If you want to keep the tank on the inside, you may likely drop the kegs from 4 down to 3 or even two depending on the size of the CO2 tank. I'd definitely follow suit and try to keep it outside of the keezer for space. He went the extra mile with his setup, so don't feel as though it's a competition. One thing I would take away from his post though is the computer fan. Keezers generate a lot of moisture which can be a problem with rust and funk growing.
If you want to build your keezer in phases, and not go straight for the collar and tap handles right off the bat, settle for keeping your CO2 tank in the freezer, temperature controller dialed in, and just use a couple of picnic taps. That'll be enough to get you started until you get the full keezer built. The picnic taps are nice to have anyways in case you ever want to take a keg to a party, and don't want to lug the entire keezer with you.
As far as kegs, go with the above mentioned cornelius kegs. Unless you're brewing above 10 gallons a batch, you probably won't need to go bigger, and if you did, you probably wouldn't be looking at a freezer like that. Cornelius kegs will handle your 5-6 gallon batches easily, and fit will inside of chest freezers. Don't bother buying new, you probably won't need them new. Just make sure you're buying from a reputable source, since they can arrive dented and banged up enough to be rendered useless upon arrival. My suggestion is to buy them from your LHBS, pressurized. While I'm speculating, I'm guessing stores can't ship pressurized kegs in the mail for safety reasons, so you're taking a gamble when ordering used kegs online. If you buy them under pressure at a LHBS, you'll know they hold pressure.