Now, to answer some of your questions, some countries are more open than others in accepting ATPL passes from other countries.
this is a pretty important point. rules are streamlined but national implementation/interpretation varies.
add an extra layer of uncertainty given current switch of licenses.
CAA is probably among the more flexible ones. (so dont assume you could also go to any other state and expect the same rule. just as an example, i dont think germany accepts UK theory credit)
I encourage you to check out Iceland as well.