For your target market, it sounds to me like you'd be much happier dealing with more mid-range stuff like Fords and Volvos rather than going to premium grade stuff. Parts are cheaper, usually less going wrong, and the customers are of course a whole lot nicer (disclaimer: I'm a Ford owner).

If you want to get into performance, I'd go gentle: Ford have sports lines of their usual mix (ST/RS in Europe), as do many other makes.

Also a small hatchback with a big engine is a lot more fun per dollar than a Merc...