Same here… first house I bought down there was bought in millions of francs…haha!
It would depend whether you are making a permanent move to France or furnishing your holiday home. Different regulation will apply. Good luck either way.
Depends on how valuable your stuff is. See https://www.douane.gouv.fr/sites/default/files/2021-01/19/Brexit-guide-voyageurs-travellers.pdf and Trouble-free travel with French Customs
Of course trailers/caravans aren’t registered in the UK (unless you get to the size of commercial trailers).
CoC can cost money, never had to pay for any for my BMW’s but I know people who have had to pay for CoCs for other makes.
Does anybody know whether CoCs issued by UK manufacturers are still valid in the EU27?