I have bought a secondhand car from a garage and a brand new car on line. Both times, it was easy to arrange insurance for the day of purchase by contacting our insurance company and the company can tell you straightaway the cost, validity, cover, etc.
Best to do this straightaway so that it's in place for the day.
As to paperwork, I am not so sure of that but I imagine that it would be the usual pièce d'identité, justificatif domicile, insurance docs and, of course, the wherewithal for payment as agreed?
Apprendre une langue, c'est faire un voyage différent chaque jour.
from Fle pour les curieux