1) Not sure on this. I think it's the same exam as each member state has responsibility for a particular subject. At the moment, the UK 'owns' humand factors and air law (i believe).
2) The UK is no easier or harder than any other JAR state.
3) To get an ATPL issued on the back of an FAA one, you need to complete an type rating and LST (licence skills test) in the aircraft type you are current in and have over 500 hours multi crew time. In your case, that would be a B737, not a MEP.
4) Really depends on you. Some people manage to complete the distance learning in 8 months, whilst still holding down a full time job. If you can study about 20 hours a week you could have them cracked in about 8-9 months.