IMC requirements
Rusty Cessna is right about the requirements, with the additional requirement that 5 hours of the 10 hours P1 must be cross-country, but it'd be unlikely that they wouldn't be I would have thought.
Also, to clarify, you need to meet these requirements when you apply for the rating, not when you start the IMC training.
Personally I think doing it in the UK is a good idea - remember that you won't have the frustration of lessons cancelled due to weather nearly as often as you do when you are doing your PPL. RT, which differs somewhat between UK and US, is more important in IMC.
As for doing it now or waiting till you've done more VFR flying, personally I don't see any downside in doing it now and there are plenty of advantages. It will improve your confidence and abilities to fly, even under VMC.