Dhwani12:
I'm sorry I can't help with all your questions, but here's the ones I can help with certainty:
4) For all my work experience, do I need employment letters, salary slips etc or is a letter of recommendation from my bosses enough?
A: No, recommendations letters are all you need. If you are accepted, there is a background check which will help verify many of these pieces of background information.
5) For volunteer work do I need to ask for the certificates or are letters of recommendation stating duration enough?
A: You don't even need recommendation letters. It's based on an honor system. You note the details of your involvement.
For your other questions, this can a good forum but you may be better off directly contacting the admissions offices of the schools to which you are planning to apply. They can give you precise answers that will limit any potential issues later.
Good luck,
Admissionado