Again in theory yes, but I drove all round Europe with mine in the glove compartment because I couldn't figure out where to stick them on Supra headlights, so it's not going to cause you a problem.
No, your car is registered here, so that's fine.
It isn't endorsable, and they have to actually stop you - if you get caught by a speed camera (not that there are many) you're fine. If you get caught you will get an on the spot fine (anything up to 500 or 1000 Euros), and they can confiscate your license. It will get posted back to you in the UK, but you won't be able to drive in France which would be a problem of course!
No, those kind of regs are all different in different European contries and are assumed to be the responsibility of the country you come from.
You don't have to carry a warning triangle, medical kit or fire extinguisher in France.
The one thing in France you must NOT have is any form of speed camera detector. They are illegal, and if the police think you have a radar detector they will rip your car apart to get at it and destroy it on the spot, plus fine you 500 Euros. In theory the GPS ones are OK because there are no French databases, but if they think it has radar detection as well they'll destroy it and let you argue about it later. So leave them at home!