Always had floor mats in mine. Might consider getting a set of the more robust rubber mats as they contain sand/dirt better and are easy to clean.
As for radar detectors you have to be very careful in Europe as many countries (such as Germany, Austria, Switzerland) don't take them lightly and if they catch you with one installed/in use you likely not only will have to pay a hefty fine but they will also destroy the device onsite. In my opinion not worth the hassle. As you're limited in highspeed capabilities during break-in I'd always recommend to enjoy scenic backroads/de-tours
Paint wise the cars are prepped and do have coat of sealing on them . I usually took a bottle of Zaino Z8 with me and applied it in the garage at the Welt . Works great and makes the following cleaning much easier. Once it arrives stateside it will get the full treatment.
If you're interested in having your car fully detailed before shipping/after pick up , there is a very good detailer within 30-40 minutes driving.
His name is Dominik Krabichler (http://www.polierstudio-münchen.de/
) and he also carries the full range of Swissvax (inside/outside products) and a wide range of supplies, MF towels etc