I guess you're getting off on the wrong foot here - Your goal needs to be validated first (for realism :) - and the water cooler chat showed other signs
Now, assume everyone from all the teams you want/have to work with gave a list of "my commitments" to you. You laid them all out on the table, what are they chances that they would be in perfect sync, perfectly reconcilable and happy-happy? Quite low, right? (Think of it as each person flipping a coin and everyone gets a heads! That's 1 out of 2^n, n = # members!)
I guess you need to have a session with all the relevant (success critical) members/stakeholders. Have them in a room and tell them the goal/problem. Ask each one in turn what they expect or what is it that would make them 100% committed toward achieving the goal. Note it on a post it and stick it up on a wall. Once everything is done, try getting rid of the duplicates if you can. Else, just read each one in turn and see if anyone finds a problem with it - if not, put it on one side, else stick a different color post it to write the issue. Do the same for all post-its. For each of the issues see what are the options to resolve them.
Now, the isolated post-its are something with no issues, pretty much what everyone 'agrees' to - (if there IS a disagreement, it has an issue!). Put a tick mark on it these 'agreed' ones. Go through the options and see which ones are agreed to by the group. Put a tick on the option and the post-it and move to the other side with the agreed ones.
Once this is done, everything on the wall should be agreed to and you'd have reconciled everyone's differences and made everyone feel a "winner" i.e. they got something out of it that would make them 100% committed towards its realization! Having a "shared" goal/commitment/vision is what it'll take to succeed.
It's a simple value equation - if they see value in the initiative they'll work towards its realization. So spend some time in the meeting/workshop to articulate/capture value and the related goals of achieving it. Only THEN do the above, else it'll be a waste! (Write that down on the side of the white/black board or flip chart, so that everyone can see it).
This should help you tremendously, it works in practice and I've tried this with numerous teams and have seen consistent results!
Hope it helps!
PS: The discussion may lead to more post-its when you are discussing issues/options or other post-its. That's totally fine and expected AND valuable!