Based on what Rex ran in NY, in 2014 for example, his 3-4 used Wilkerson, Snacks, and Richardson on the interior, then Coples, Davis, Harris, and Pace. Pace = Hughes and Coples = Mario. If they pick up Davis, then he and Brown in the middle, with Lawson (in Mario's spot for now) and Hughes on the outside. For the interior 3, Dareus and KW at ends, then you need a true NT in the middle.
i think the #1 need is to replace Mario's spot. They will also need someone to replace KW next year, and spell him a lot this year. They'll need another LB in passing situations if they pick up Davis. I think they can find a space-eating NT in the later rounds, if they don't already have one on the roster in TJ Barnes?
In R1, I think they'll go with the BPA between the Mario replacement and the KW replacement--seems to be where the most talent is that will also be available at the pick.
My thoughts at least.