Hi, regarding the vehicle I think you've already answered your own question..
If you can use a UK address then buy something in the UK. The only 'sticky' situation may be finding suitable insurance cover (most insurance companies have a time limit on mainland european cover) - registering in the UK is a formality, but re-registering in France can sometimes be a bit of a palava, but not too difficult if you have some patience - the French system is full of red tape.
Good luck!
If you can use a UK address then buy something in the UK. The only 'sticky' situation may be finding suitable insurance cover (most insurance companies have a time limit on mainland european cover) - registering in the UK is a formality, but re-registering in France can sometimes be a bit of a palava, but not too difficult if you have some patience - the French system is full of red tape.
Good luck!