As a CS 20.3 owner I'll try to answer some of your questions:
1. Regarding the keel (actually I think a better term would be a skeg since it isn't a proper keel): Alan approaches his boat builds from a racing/hydrodynamics mindset, so he left the skeg off for a slightly faster hull. Most CS 20.3 builders attached a small one, myself included (I added a stainless steel hollowback to it as well). My thinking was that it could take some abrasion from beach landings and also register in the grooves of the trailer rollers.
2. Ice chest: it is drained through a small tube into the self-draining cockpit. I would highly recommend building in the ice chest. I did not and regret it; my portable cooler keeps getting in the way. I actually asked Graham about it yesterday; he said on his last trip the ice lasted 5 days. Lastly the ice chest does not in any way interfere with sleeping.
4. Buying CNC machined foils from B&B versus shaping your own: given the importance of good foils I would buy the CNC machined ones; it will save you significant time and you are guaranteed good ones. I made the centerboard myself using templates that B&B kindly provided me, and bought the rudder, but as a handplane collector I wanted the opportunity to put them to use. If you are not an experienced woodworker I would just buy them.
5. Bunks: they are comfortable and very long. I just spent 6 days sleeping on the boat and slept well. There is plenty of footroom, and I like the space behind the bunks; when you wake up in the morning you can just stuff your blankets behind the bunk for the day and they stay clean, dry, and out of the way. For reference I am about 6' tall and weigh 165lbs.
7. Centerboard location: your kit or plans will have the updated location. It was only us very early builders (we started building before B&B even really finished the complete plans) that were affected. I just finished a 5 day sail with another 20.3 with the updated location; he was able to point a little higher than me.