2...What airport to use ... I live in USofA, WashingtonDC
..don't wanna go out of BWI, unless i must

I live in VA and have flown to Sangster from IAD, DCA, and BWI many times. Southwest flies non-stop from BWI and it's worth the 90 minute drive to get to BWI to get that flight in our experience.

12..Am on a tight budget --- for food, wanna spend no more than US $10 per day [or less] .... ??..do-able..??
Not doable for me... but maybe. It would be very tough especially if you are shooting for 3 meals per day.

Best of luck!