Shortly after Boxflyer and I finished filming the 20000Km service on the Wethead RT, a K13GT rolled in for a similar service. This is involved, but there is no great mechanical skill needed. You will need the Service DVD, a decent torque wrench, a vacuum coolant filler, and a few special tools from BMW. Even after buying all these tools, you will probably still save money over paying someone else to do the job.
There are a few points to be cautious of.
1) make sure the cam chain retro-fit has been done on your K13. This is truly an ounce of prevention to avoid a ton of cure.
2) Don't avoid buying (or making) special tools for the job that you will see in this video. They work, and work well.
Most of this video surrounds the valve clearance checks. Some of the special tools you will need ONLY if your clearance is off. I would avoid actually acquiring them unless you need to make the adjustments-- for that reason, i would suggest you undertake this service when you know that you are done riding for the season, as the special tools can take a LONG time to arrive. From my experience , the K13 rarely needs adjustments-- so, again, hold off buying the tools unless you know for sure yours are off.
As mentioned in the intro, I don't show all the components of the service as they are simple and strait forward (oil change, for example).
As far as time allotted to do this service, front to back, it will take you a full day at a normal pace. If you actually need to adjust the valves, add an evening to that.