Well needs to decide with the ATPL theory part first. Not sure unless he speaks good greek, if it would be good idea to do the ATPL theory in Greece!
From the outset with some exceptions CPL/IR must be done in same country as your ATPL theory.
Sure exams in Greece will be in English, however you also have to deal with their CAA and do a course for the theory there, not sure about that, but need to check this to make sure no major issues.
Also I would be a bit worried to advance to much money with a Greek company in these days, at least try to keep any advance payments as low as possible, in case a collapse in the economy. (bigger collapse)
Being from Norway, I know they are a bit more detailed with their paper work when doing tests outside their country. I know ATPL's taken in any country other than Norway, will never be accepted in Norway. Had UK ATPL theory, and was easier and cheaper to do it in the UK.
ATPL theory depends on type of course, distance learning or full time, I know London Met and Oxford do modular ATPL theory courses, I would recommend these. However with British ATPL's, you would normally need to do your flight training in the UK, unless you apply special for other country.
Many companies prefer CPL and IR done at same school, so should have think of this too.
Not sure if savings will be so great though around Europe, looking around to countries where you might run into other practical problems. I know Norwegians normally speak good English and some German, and I would tend to recommend a school that is strongly linked to these languages. Cheaper than Scandinavia, and good quality training!