Sometimes we get so focused on our teams and our experience that we put blinders on to what WifS has to consider for all users (and potential users) of HBD. Right now HBD borders on the line between awesomely in-depth and overwhelming for new users.
Your FA process proposal would be cool for those that have the time and have a good grasp of all other elements of the game. It would a pain in the rumpus for others. But as to not throw out and trample on your suggestion completely, here are some thoughts...
1) The GM could query the agent/player for their initial demands. Sometimes the agent declines to state his demands, sometimes by querying the player might unrealistically raise his demands in an attempt to squeeze out more money.
-This is the part that I would find frustrating, and ultimately a waste of time. If I like a player, take the time to query his demands, then find out that he's asking $5MM more per year than I'm willing to pay him, that would quickly become less than fun IMO.
2) If an offer to a player is close to their demands salary wise, but off in years (or vice versa) the agent might state that in his response ("The annual salary is close, but we want more guaranteed years").
-The way I understand the engine to be built, the player is more concerned about dollars and less about years. I'd be in favor of average annual salary being the deciding factor. After all, 3/45 should be preferred over 4/45. I can't be sure, but I'd say that today those are treated the same.
3) An agent could throw back a counter offer, and if accepted by your franchise, it doesn't mean the player is automatically yours. The player could still hold out to see if somebody else tops your deal.
-Today, the player lists their MINIMUM demands, which is why he won't accept less. To accommodate for a negotiation process, the players' initial demands would have to increase so that you'd be able to offer less, though his minimum would remain the same. If no one offers their minimum demands, they drop them (which does happen today). So this may feel neater since it feels like you're negotiating, and it may be preferred by some, but I think you'd end up with the same result.