I can't think of any occasion where hours logged PiC for the CAA would not count for FAA, nor vice versa. If you do military flying they might want to only consider that, but they'll give you their own logbook anyway.
You can end a logbook and start another whenever you like - so no problems there - I'd just recommend removing or crossing through the pages you aren't going to use.
Regarding separate logbooks, it's a perfectly reasonable thing to do (even if I don't do it) for different classes of aeroplane but I really wouldn't recommend doing so just for different authorities. Aeroplane (or helicopter, glider...) hours are aeroplane hours, the country and registration are pretty much irrelevant to your total currency and flying experience.
It really does not matter which logbook you use for gliders (you could even use a British Gliding Association logbook!), just use different columns for PiC and PuT, which in turn are separate columns to those used for recording other flying.
Trust me, it really isn't that complicated - don't get worried about it or over-complicate things unnecessarily.
G