Now I've been building Ribble bikes all morning....

I wouldn't be too concerned at all with ordering a bike from the UK. It sounds like you have the experience needed to do your basic maintenance and take care of any smaller problems that may arise. It just comes down to whether or not it's a chance you'll take and if you like the prospect of the bike enough. I did the same thing two years ago when I bought my Cube Cross Race from a UK dealer. No support in the US meant weeks searching the internet for fit reviews and advice, plugging numbers into online calculators, and evaluating all the components on the bike. I do most all of my own maintenance, and can build from the ground up, so I was confident I could take care of anything short of a wrong frame size.