Regarding validations, I believe the UK can and has offered validations for 12 months for specific requirement crews. (ie Airline X needs pilots with Y experience) To continue beyond the 12 months you must complete all the exams.
The UK CAA will issue a JAA ATPL if you have 3,000 hours or more with 1500 hours in command of a 30 tonne or greater jet in primarily international or equivalent operations. You'll need to sit 2 JAR exams and an observed skills test on the type you want to open your licence with (and you have 500 hours on that). This licence will be only valid for G reg aircraft, you want to fly for any other state and you'll have to complete the remaining 12 exams.
All this must be confirmed with the regulatory authority concerned.