General thoughts, that is too many CEL's.
I have had the brake switch replaced, fairly common, as is the fuel lines/O-rings. Not certain about cruise control dying. Thought speedo was electronic and if that went to zero while driving, normally a "Display Defective" issue. That happened to me once, restarted car and never again.
Sorry, no background on the K-40 relay, new one on me there.
Mine has never left me stranded ever. Did have the MAF go bad and got a CEL on that.
I posted a thread the other day that basically got minimal attention. It was about as a W210 owner I think CEL's are more common. Had one the other day, turned out to be an EGR flow issue, but it was 8 degrees out, so probably just gunked up and cold and need to do the big cleanout job. I am looking at getting some type of a diagnostic scanner, so I can simple look at it right then and make up my mind if it is a big deal or not, clear it and see what happens. My bride paid the dealer $92 to check and clear a code basically. Well that would have been better spent on a quality tool.
Here is a link to decoding the codes, though one you mentioned is not on here?
http://www.obdii.com/codes.html