Hi Pa31t, happy new year. I am not able to answer all of your questions, but I'll try my best.
1- I'm not sure but I don't think so.
2- It depends on you as you need to sit the 14 EASA ATPL exams. I reckon that holding an ICAO ATPL you are not required to take the whatever minimum classroom-hours needed to sit the exams, however I strongly suggest that you follow a course. I understand it is at least 6 months. (Bristol GroundSchool, which I recommend).
3- Yes, however you are required to pass a check ride.
5- Talking about the ATPL theory I guess around 3000 pounds? Double check on BGS website.
6- Sorry, I did not get the question.
8- I'd say the UK CAA, and I heard the Irish CAA is also not bad to deal with. You may want to verify whatever is cheaper for you and then convert the license, it is not cost free, obviously. I would avoid both Italian CAA and Spanish CAA.
