Lovely car. Funnily enough I bought my CL500 in exactly the same colour on an impulse purchase a couple of years ago.
To give you an idea of the running costs, if the 4.3 is like the 5 then you'll be looking at the cats in the exhausts going at around this mileage - mine did and I hear it is very common. Costs about £2.5K to get it done from a Merc main dealer but under a grand if you know a friendly independant. Servicing from an indy is about £400 for a minor service and double that for a major one. Brakes and pads all round for me was about £500 I *think* (don't have the invoices in front of me) Keys are about £80 - £150 depending on whether you want a keyless go or a proper one and I can't think of anything else I've spent on except normal consumables. Hopefully you'll see better than my 18mpg, although probably not by much!
I think they're pretty well put together considering it was Merc's worst period for build quality. Hope you have a good time with it - you'll have great fun leaving hot hatches in your wake at traffic light GP if that's your sort of thing. They never expect people in luxobarges to pull away smartly at the lights.