I have size 15 boots and have used the Burton Ruler's the last couple seasons. They've very comfortable, and with Burton's shrinkage tech the exterior footprint is that of a Size 14 boot -- every little bit helps when you have feet our size.
As for boards, yep, wide is definitely the way to go. I'd also recommend a duck stance (-15/15 or similar) as this will reduce the amount of heel/toe overhang.
Finally, yep, you'll have some degree of overhang, but for instance I ride a 169 Burton Custom with the above stance setup and my overhang on the heel/toe edges is roughly 1.5-2cm each side.