To answer your questions, my opinion:
1. Many teams, especially attacking 4-3s like ours, run defensive line rotations/frequent substitutions. This includes Seattle, Atlanta, Philly, Dallas, us. etc.
2. Any given Sunday, I'd expect our starting 4 would be: Hughes, Star, Oliver, and Shaq (barring injury to these men)
3. Murphy, Yarbrough (as of now) and both Phillips get used in the normal rotation (non-situation driven)
4. Obvious passing situations, I would expect: Hughes, Oliver, Zo, and Murphy. This is the wide 9 grouping, minus Kyle that they ran last year. With Kyle lined up next to Hughes and running frequent Texas stunts
5. Obvious short yardage (goal line): i would expect all 4 defensive tackles on the field, along with 2 defensive ends. Typically aligning the tackles in the 1 eye and 2 eye techniques
Any attacking 4-3 system requires basically the equivalent of 2 waves/rotations. Because they are asked to penetrate and shoot gaps every single play, they should never be taking a down off and gives them more opportunity to stay fresh for the entire game.
Regarding Oliver, it is very obvious that we needed a 3-technique to replace Kyle. Oliver was the best option to fit in our defense.
Not that we had the choice, but I still thin they would have drafted Oliver over Allen. Oliver plays the 2nd most important role on Mcdermotts defense (behind MLB). And based on his pre draft comments, inside pressure was a focus