Like it or not, Brexit is happening.
As the UK is the first member country to leave the European Union, we’re all heading for uncharted territory, and we don’t know, what we don’t know.
Until things become a little clearer, particularly relating to UK citizens currently living abroad, there’s little concrete advice being offered. One thing for sure is that we’ve always travelled abroad – it’s in our DNA, before the EU and before the days of the British Empire.
For new arrivals I would suggest a trip to your local Mairie to obtain a certificate of residency, to give an arrival date in France, and to learn French as quickly as possible to better integrate into local life.
As we are still EU citizens, there is no need to obtain a Carte de Séjour, although it can be obtained from your local Préfecture. If you are specifically asked to obtain one, my suggestion is that you query the need to supply one, as the UK is a member country, but if this fails, look at https://www.service-public.fr for full information. The documentation should be the same wherever you live, but this being France, things get interpreted differently at different offices, and by different officials.
Please call me if you need help in any way.