If your uk based you could live and work in Ireland if you want with a EASA licence, Ryanair operate mostly EASA registered aircraft’s out of the uk instead of G- reg and so require either EASA or dual EASA/CAA licensing.
As far as the 13 ATPL exams the material is mostly the same, you will have to sit each exam twice if you want to obtain both EASA and CAA exam, I believe you can do the Austro control Austrian EASA exams and the CAA exams in Bristol.
All of the training will be the same but you will have the added expense of sitting the IR twice if I remember correctly, along with dual medicals. I’m not too sure if hour building on EASA registered aircraft’s is valid across for CAA validation though.