Sorry, zoro, but I just typed a long reply, only for it to be another of my replies that has disappeared into the ether. I'll give it another go, but am getting heartily sick of this!!
1. If its a container grown plant any time is the right to plant. Bare rooted, in the UK the best time to plant is October/November so long as there is no frost (which I would imagine would not be a problem in the Dordogne.
2. France, being another EU country, I believe there are no restrictions on plant movements.
3. The Bramley apple is a triploid, which means it needs two other varieties to pollenate it, to get any fruit. There may be other apple trees in the vicinity, so you may not need to buy any other trees.
Bramley apples tend to be large, so do not do very well on dwarfing rootstock - the weight of the fruit can break the branches.
Hope the above is helpful,
valmarg