If buying a used model, don't all these rules and regulations depend on whether it has been registered by its current owner under CS-VLA, CS-22 (glider/powered glider), or locally as a ULM/ultralight/microlight.
If the aircraft is currently registered CS-VLA, a lot of the licensing issues disappear, EASA aircraft and EASA licence, so just get your SEP renewed/revalidated on your British ATPL, and then you can fly it home on its current reg.
If registered under CS-22, similarly, wouldn't you just need TMG class rating added to your UK license, and it could then be flown home in its current reg?
If registered locally as ULM... I have no idea, see advice from people who know about that sort of thing.
However, having done some cross-European VFR flying in a rotax powered VLA (very recently), would be happy to advise on some routing/night stops worth making!