The chat and the stud check are different. Most do studs, then ask the FRs, #9's and perhaps #10s to stay behind for the chat.
The only absolute is to tell the front rows how you will manage the engagement sequence. After that, I think the #9's find it useful to know that you expect a feed down the middle, and that if they want to tap and go at a PK they should do it from behind the mark, and within about 1m. Remind them that you may be focusing on other things, and that if so they'll be called back to have another go. Equally, if they have to dig the ball out of a ruck, you'll protect them until the ball is off the deck, but then they're fair game.
#10 - all I need from you is to manage the offside at scrums and lineout. At lineout, I'll try to give you a raised arm to keep you back, dropping it when you can come forward. But it's your responsibility to keep them all back until the lineout is over. I can't help you at scrums - I need you to keep them back 5m until the ball is out - especially if you lose the hook against the head.
Questions?