1. Working experience can be defined however you think is most reasonable. From my perspective, I'd probably say the internship and social service could potentially be classified as work experience (and maybe even your practice/rotations, depending on scope and level of commitment).
2. No. As an international program, Wharton accepts students from all over the world.
3. Use your best judgment. If you were doing it full-time and got paid for it, that probably would be work experience.
4. Carefully reading many of the threads in this post and looking at the Admissions website. Have a solid answer for "Why do you need a Wharton MBA, now?" and think about how this will come out in your application materials. Think about how you will write your essays.