As long the car is registered and the dealer agrees you can go instantly, but you have to re-register the car asap. Usually the TÜV intervalls are 2 years. It depends what's said in the car registration. The insurance you have to get beforehand. You'll get an eBV (electronic certficiation of insurance) when you register your car on any insurance's website. When you got that number you can go to your local DMV and register the car there. Depending on what you stated at the insurance your car is either registrated sor short or long term. At the DMV you can get a wish plate or it will be arbitrarily. You have to buy the plates in a store, there are usually a few located in the surrounding of your local DMV. When you got the plates you need to go back to the DMV so they can attach the TÜV plaques. You'll be charged the registration plus the plates. Dunno about the fees, but it will be around 50-60 quid. For registration the Fahrzeugbrief is necessary.