Yes. They will.
I have just purchased the very same wheels for my C230K, but bear in mind that the rears are normally fitted with a 225 and a lower profile than the 205 fronts. Although I don't think you would notice much of a difference with the 205's fitted all round for normal everyday driving.
No - as Nick says they are SLK alloys - hence the 170 part number - standard sport alloys have a 202 part number.
The differences are very subtle, the shoulder on the spokes is rounded on the C class sport alloys, but has a much sharper edge on the SLK ones (at least I think they do). Normally I think the SLKs are polished and lacquered, rather than the paint/lacquer of the C class sport (normally difficult to tell the difference on e-bay photos unless they are close up).
Yes they will fit - I did have a good look at these (on my watch list) as I'm looking for a couple of spare wheels to diy refurb as the tyres wear out.