You might get some additional feedback if this is also posted in the "Hot Rod" section. The 500E owners are generally active in replies.
As for any advise from myself, depends on what you want? Do you want a car to work from or do you want it to go another 100k? These cars if maintained, do very well, but..., like you said, a lot can happen in that many miles.
If you are close geographically and have a "Warm Fuzzy Feeling" about the car, spend the $125 on a thourough tech inspection at a trusted MB shop and go from there.
96 C280, Greenish Black