good idea to buy a bike in Germany instead of shipping your own bike over.
* getting your money back from the ADAC should be not a problem if your carnet is complete and filled out correctly, but it can take some time.
* a normal German rego is valid until you go to the rego office (Strassenverkehrsamt) or you send your plates back (to get the stickers removed), so you wont get eight month with an expiry date. But you can not get a normal German rego in your name, because you dont have residency in Germany.
* you can get an export license plates (export rego), but I dont know for how long this is valid in Europe.
*your carnet is valid for one year, and this will be your document to cross borders in Asia.
*my advise. you dont need a valid rego if you are outside of Europe, only the carnet, and of course a paper that looks like a rego if somebody ever asks.
*insurance. you buy or you dont buy at every border. For Europe (included Turkey) your German export rego requires an insurance and from this insurance company you will get the Green card valid as long as your exports plates are valid.
somebody else here on the HUBB to answer radioactiveangles question more precise ???