I was in the same situation as you, 3 years ago. It was a bit of a dream car.
To be honest, I'm not going to be much help for you here - I've had it 3 years, and the only problem was a stone-holed air con rad. So, on my experience, I would tell you they're faultless!
You're right that the head bolts is the only very prevalent issue, and that the facelifts are not prone to it.
My main piece of advice would be to join the C63 AMG UK facebook group - that has a good buying guide in the 'about' section, and lots of helpful people too.
A lot of people say an LSD is a necessity - and it certainly does spin the rears easily - but I've managed without for 3 years.
People who tell you rear tyres only last 2000 miles are people who drive like idiots everywhere. I'm like Miss Daisy half the time, and my first set lasted about 12,000!
I've found servicing to be not bad at all - but then I use a well reviewed independent specialist. First service was about £600 - but I got them to do all the plugs at that one, so it was cheaper than I expected. Second was £300. Third was £500, but involved extra work tracking down the aircon fault.
If you get an estate, on at least one occasion try driving along with the boot open a touch.