Your post is well thought out.
I disagree with you on Safety. Losing Poyer & Hyde is a major downgrade. Yes, it was time to move on from them, however Edwards has mostly been a back-up and is a big question mark. Rapp I thought played better in the second half of the season. So there is some concern at this position. I do think that we will draft a Safety.
At Defensive End, losing Floyd was big. Glad that Epenesa was kept and I like Casey Toohill as a situational pass rusher. The draft is thin at this position, so it won't be easy finding a top grade player. The Bills could find a veteran late this year as they did with Floyd.
Wide Receiver is definitely an issue. The Bills pretty much have no choice but to take a receiver with their first pick. While Diggs declined late last year, be it from talent or injury, his leadership(he was a captain) will be missed. I love the addition of Samuel, and I believe that Shakir will continue to improve. I don't like to rely so much on rookies, despite how talented they are.