Used car, register – re-register – unsubscribe hä ?!

Hello together, so I would like to buy a car have already telephoned with the owner (private person) etz.. Supposedly it comes to the purchase, unfortunately the place is 200km far away. So I go look at the car, do a used car check at the TÜV – everything good. I conclude the purchase contract, pay the vehicle, get the papers and log it off at the registration office. Problem, where I leave it standing until I have requested the transfer registration marks and back there b in whr. only a few days to a week later? Because I can’t leave it in a public parking lot if it’s unregistered? (When the vehicle is unregistered, the registration plates are also handed over?) Can I just log off a vehicle for a few days? Or do I have to register it right away, stupid because I only take out the insurance after the purchase? So then I pick up the vehicle with because overpass registration marks drive to me and report it at the registration So briefly how does the whole story look with born vehicle bought and then ?! Thank you for reading Maybe one or the other can help me am really overwhelmed !!!