I did just this very recently. I was in CA and bought an 11" MBA + Applecare. Even including CA state tax, it worked out considerably cheaper than in the UK or in Austria where I live now. Most of my electronics have UK plugs and I have to use convertors here in Vienna anyway so having a US plug doesn't really bother me that much.
As others have said, Applecare is an internationally recognised warranty which is also taken by authorised resellers, a good this as there isn't an official Apple store here in Vienna. As for the keyboard, if you really want you can order one and have it delivered to the local Apple store for you to pick up but TBH, the differences between the US and UK keyboard are pretty minimal. You may not be able to find the exact configuration you want in store so ordering may be a requirement.
When you take it back, just have the laptop in your carry on and you can put the box in your checked luggage.