Thermostat is fairly easy -- unless it's located in some oddball place. Depends on the engine. On my M104 and OM606, it was a 20 min job.

Fan clutch, on other hand, is a little bit more complicated. As others said, you need a short hex bit. Both of my cars were hex, though it's possible that newer cars switched to torx.

It's a bit easier if you unbolt the radiator (from the top) and push it back a little bit. Don't have to open it up or remove it or anything, just push it back 1 inch or so. Gives you a lot more room.