I don't have any advice on cleaning it, but I'd recommend buying nice 1/6 kegs unless you are having a party. A keg will keep well over a month or longer as long as you've got CO2 and keep it cold, but that's still a lot of beer to go through unless you've having guests over. Roughly 160 beers in a standard half keg (or 120 pints). Get the 1/6 kegs and they go faster and you get to try more beers. With the exceptions of huge warehouses, most places don't stock anything beyond Yuengling and Miller and those types, so you'll probably be asking for special orders for any keg you stick in there anyways.
Also, get a double-pressure gauge regulator. That way you'll be able to see on the gauge how much CO2 is left in your tank in addition to the outlet pressure (you can look up what psi each brewer recommends their beer be set to for various beers if you like, or just keep it somewhere around 12). They usually last for 2-3 kegs worth of beer, but nothing is more frustrating than getting a new keg in the fridge and then running out of CO2 as soon as you start drinking it. Test your lines for leaks with soapy water. If your system is leak-free, then you can just leave the CO2 on all the time.