Patrick Chung and Josh Barrett are more SS types, although Chung can play some FS. People forget that Barrett was starting at the beginning of last season, before being injured. Gregory who was signed, is a more of a FS and has started there, but he has also played some SS.
Edelman I would think as an ex-QB and a very good tackler and a fast and quick PR, would more reasonably be a FS type. Will Allen was a CB who was converted late in his career to play some Safety too. That gives you five candidates and you can add McCourty as an emergency #6 Safety, too.
I think Edelmen is the most logical candidate to back up or compete with Gregory for a starting FS job. He is almost already guaranteed a spot on the TEam, due to his PR ability so his FS contributions will be gravy, and provide the time for him to learn.
Theoretically, Alex Gonzalez is a better slot receiver to back up Welker, as a former #1 draft pick, if healthy, but having Edelmen around as a #3 slot Receiver adds depth there too.
The Defense is actually pretty young, and now has some experience, and actually showed well late in the season and palyoffs. I think it is ready to step forward and be pretty good. It could use some more depth.
If you look at the LB corps it arguably has more talent and depth than in many a season, both inside and outside. So does the Defensive line. The DL is far from the Seymour Wilfork, Warren level of talent, but what is there is not bad.
The secondary was pretty heavily injured last season, but there is still talent there, too, and I think the FS situation is already solved.
I have a premonition that BB is preparing to go for it all, in the twilight of Brady's career, and could confuse everyone and draft a DL, OLB, ILB and DB with his first four picks, to add even more depth.
This team could be a 19-0 squad...