If I were to build my coil box all over again, I'd get everything from the site that hosts this board...micromatic.com.
50 foot coils are not the best for keeping constantly flowing beer very cold - the beer just doesn't spend enough time in the coils. You need to base the length of the coils on both the temp of the beer you'll be serving and how constant the tap flow will be.
Go here to buy boxes/parts/kits and there's a good explanation of the differences between the 50, 70 and 120 foot coils. I went with a 120 because I didn't want any issue with beer temp and I'm glad I did. I never have to worry about keeping the keg cool and I can pour pitcher after pitcher if I need to.
http://www.micromatic.com/draft-keg-...io-cid-11.html