Advise on which Variant to pick?

I suggest you look at the respective examinable documents. I personally think that INT is "cleaner" than having to consider also UK-specifics. If however you aspire to hold a practicing for audit (i.e. you want to be able to sign auditor's reports) you will have to have passed AAA-UK (or Irish). (Though you could sit that post-qualification.)

I believe that it is possible for members to sit UK variants post-qualification.

Are the lecrure relevent to the international Audits?

@njivan28 - see in the list of notes and lectures here https://opentuition.com/acca ... Advanced Audit and Assurance (AAA) (INT/UK)