I'm playing around with this in my current Dynasty.
http://www.operationsports.com/forum...-win-baby.html
Unfortunately, there are some limits as to what the GM will do. If you sim the draft, or advance to my next pick, GM will make trades and selections. It makes for a pretty different experience to only set the draft board and let the GM do the trades and selections. They often do some crazy stuff, but it definitely makes it interesting...and then you have to work with what they gave you, instead of getting to hand pick your guys.
Unfortunately GM won't negotiate contracts or even pick who to negotiate with. The Owner will set goals for you to resign certain guys sometimes.
I've also never had the GM initiate a trade outside of the draft.
You can let the GM make roster cuts in training camp, but they generally do a poor job of it, and that is traditionally more the job of the Head Coach.
I definitely recommend letting the GM do the draft, it can make for some interesting results and really forces you to pay closer attention to your draft board...at least it did for me. Be careful though as you have to use Advance to my next draft pick to get the GM to trade (or I assume any of the advance options?) and if you do, you can't adjust your draft board on the fly. I don't know if draft board adjustments when it is your pick will affect who your GM suggests, as I think he makes the suggestion based on your board when your turn comes up, not when you click on see his suggestion. Could make for some interesting testing to see how it works.