I do not know whether Belgian CAA has PPL (A) Theory Question Bank in English, but I can suggest one way for you.
You can take theory exams under Austro Control. They provide PPL (A) Question Bank (English) in their web site. Their QB is really helpful and the number of questions is not much.
75-90% of the QB is same with real exam.
You can do your flights in Belgium. When you are ready, you go to Wien in order to take exams. You can take all exams in one day.
As far as I know, authorities accept PPL (A) Theory results taking in any EASA country like ATPL (A) Theory results.
Just a suggestion.
