50 to 100 BTC per week is indeed doable through major exchanges such as Bitstamp but you will need to pass their KYC/AML requirements which takes time. Then of course you have these German banks which traditionally restrict payments for bitcoin-related transactions. They usually err on the safe side and decline the transaction and ask for a pile of documents. Especially for 100 BTC or something like EUR 350,000. Lots of questions for sure.

Cash is just as suspicious and worrying. It will be difficult to find someone willing to meet at a Hauptbahnhof to do the deal.