Driving priviledges aren't handled by the US government, but rather each individual state.
Based upon the state you move to, you will have to comply with that states laws to get your driver license and your vehicle registered and insured.
Here is the process when you move to Florida:
- Get your Florida drivers license.
- Purchase your vehicle (the process typically includes vehicle registration).
- Purchase your Autoversicherung through CarInsurance.com.
If you have to go back to Germany or need to leave and come back you should be able to keep your license in force until you return, depending on your length of departure.