I think the bench should change according to the teams needs. This should also apply to the starting line up as well. No cut and paste please. We have the depth to rotate players.
For the starting line up I'd start with Host and have Simms and Ah Mau as bench replacements to keep the momentum going when, Frizell, Vaughan and Graham are rested. I would have one of either Latimore, Lawrie or Allgood as another prop rotation depending on whose performing the best at training. Kerr could also be in the mix as a Prop rotation. (It' would be great encouragement to give him an early opportunity)
I'd lean towards four forwards on the bench but would be flexible, taking into account individuals durability. Eg, early on our forwards will be fresh (especially pre ,rep games, niggling injuries etc) and three forwards on the bench may work well and allow Field for example to be USED as a impact player. Later on, and to prevent burnout I'd have four forwards, and have Mann as the starting centre/wing (as he could cover fullback and halves if we someone goes down injured) The other factor I'd consider consider before finalising the squad is our opposition. If they have a powerhouse pack I'd definitely match it with four forwards on the bench and use them all. I'd like to see some variation, some little tweaks and experiments eg have Robson on the bench and bring McInnes off for a spell and give Robson a chance to rip in.