planning a year for my 1st ultra

Hey,
Trying to think way ahead here. I am looking to do my first 50k (Hood 50) and 50mile (leGrizz) in the summer/fall of 2018.

This season I am doing 2 trail 1/2 marathons and a trail 30K in the fall (as well as a bunch of shorter events). This all comes after about 5 years of checkered health, two near death experiences and non-running.

My question is...prior to the training plan I'll start next spring what should my winter look like ideally. Mileage, structure, etc.
Thanks for any advice.