230 and 320 have 16" wheels as standard (but different styles) and the 32 has 17". But some owners put 17" AMG alloys on their 230s or 320s as an option when new.
Like Papa said, there are loads of SLKs for sale so there is not need to rush in to buying one.
Not sure how many Special Editions are in the UK (there was also a similar Final Edition a year later) but for your budget you are not far off the price of the SLK32 which is rare (only 271 released in the UK i think) but there are always some for sale if you are prepared to travel...plus would be a lot of fun on those roads in north Wales
And i was thinking the same about the tyres, if they are below the legal limit then I thought they weren't "fit for purpose" so they should replace them before selling the car.