Moving to Germany

We now have a chance to live in southern Germany for a couple of years, . . . . retired . . . . any information about long term visas

That is a contradiction. Do you or do you not have a valid visa? If you have not yet investigated the visa issue and are not yet confident of obtaining one, you do not yet "have a chance to live in southern Germany".
Unless you are an EU citizen, you need to contact your nearest German Embassy or Consulate and find out how to obtain a residence visa. In order to get a visa you will need enough funds to cover your stay, including paying taxes and German medical insurance.

As a resident you can buy a German registered car under the same conditions as any other German resident. Your profile says you are from "roanoke, va, usa". US licences are only valid for a limited period as tourists. Once you become a resident you will need to pass a German Driving Test in order to get a German Driving Licence,

If you are from Virginia you are very lucky to be from one of the states which has full reciprocity with Germany regarding your driver's license. This means you can trade your Virginia license for an EU license without taking either the driving or written test. You can really only appreciate what a big deal this is if you moved to Germany from a state with NO reciprocity. You are allowed to drive on your US license in Germany for six months. On day six months plus one day, you must have a valid EU license...or start figuring out the bus schedules. Your German insurance company takes this very seriously. Best of luck in your new adventure. Hope it works out for you. Our five years in Germany as corporate ex-pats were wonderful. I was very grateful the company paid someone to handle our visas, residence permits, shipping containers, etc., because that part was complicated!