Again, no answer to #1, but for #2, I've had mixed experiences. One club that positively encouraged you to claim it and one that got all ratty about it. Guess which one I'll be hiring from for future international trips??
Just ask around beforehand, should be ok as long as your club ain't run by a bunch of cowboys. Also check the club rules, it'll probably be in there.
Oh, and its not actually VAT drawback, its fuel duty drawback 27.34p/litre last time I looked and make sure you claim it on all the fuel in your tanks (bought in the UK) not just the amount you use on the outward trip.