Some specific follow up questions:
1) So if I understand this correctly, if you did well on Step 1 it is best to take Step 2 CK "later."
Generally speaking, this is correct. It does seem that the definition of doing "well" on Step I has been creeping upwards recently. I would say that if you're >250, this certainly applies. 240-250, depends on the rest of the app. <240, and early Step 2 is advised especially for the more competitive programs.
One poster said January? It sounds like most interviews fall in the December/January time frame so do you just study as you can during those couple months then take it in late January?
I took Step 2 CK "late" because of the aforementioned criteria, but early enough for rank list because I was highly interested in a program that required this result to be ranked. Thus, I took it around Christmas time of interview season. Studying for it in the midst of frequent interviews, airports blaring carols, cross-country plane travel with time zone changes, etc. was rather hellish and I would generally not recommend doing what I did, though I ended up happy w/my score.
If programs requiring this score are high on your interest list and you intend to take it "late," I recommend taking Step 2 CK before interview season is in full swing (September/October/early November) so that you have control over your score release but are not studying in the midst of heavy travel and interviews. If these programs are not high on your list, defer to post-interview time when you are more relaxed and the score doesn't really matter providing you do ok.
2) What about Step 2 CS? Is that required to go into Match week? A good portion of people from my school take it during spring break of their third year, and I'm curious what everyone thinks about that...
Again, depends on the specific program, but with only one exception that I'm aware of, the answer is no it is not required. This one I would take early just to get out of the way, because the amount of studying is minimal, you're fresh off your third year rotations and can do an H+P efficiently, and if you do fail by some fluke, there is enough time to retake. Also, the scores take a much longer time to come back. As I understand it, programs tend to care the least about this score, though it is advised for financial and other reasons to pass on the first try.
If you do take this after match and fail, your time to remediate prior to internship is more limited - though again, as I understand it, in many states you can start PGY-1 without passing CK.