$100 can get you the same day service....submit before 11am and get the visa at 12 noon. Be aware of the possible long lineup at the embassy. Be sure to have all the required items (photo, pre-filled form, passport, old visa/passport, etc).
I don't think so, as long as you check the multiple entry option on the application form, it will be Ok, and you just need to pay different application fee at the end.
I don't remember the details, but I don't think there has to have specific reasons to apply for the multiple entry visa.
But, it might be depended on the officer in the visa office I guess.