I believe its a 7/8" bit for the door. I have a step bit that I used for holes, but a metal hole saw is cheaper. I personally got a tap that had 5' 3/16" tubing and I only get a small amount of foam on the first pour, but that's because of lack of cooling in the tower.
Kegging is all in all quite simple, you just need to read up on it a lot and understand the process.
Secondary #1: Mead Experiment
Secondary #2: Welch's Wine Experiment
Kegged: Organic APA, Kick the Bucket APA, Pub Ale, Argentine Cascade IPA, ESB
Bottled: Wild Raspberry Cider, Cyser, Insane IPA, Lady Bug Pumpkin Ale, Cider, Christmas Cider.
RIP: Raspberry Hefeweizen, Hoppy Lager, California Common, Oktoberfest, Hefeweizen, Melted tubing brown ale, Honey blonde ale