#4 is the most important on the list. There is someone championing this. You must figure out how they are, and what their motivations are. Not only to help the deal through, but understanding their motivations will help you understand if it's right for your team.
Are they buying you just to get you out of the way? Is that ok with you?
We seem to be ok with #4 so far, but we'll see. They'd be buying us for our technology and staff, we've gone really far where they want to go and I've had an intimation that they've put some R&D into it already and figured out that it's pretty complex stuff to do well. It's been an honor to have so many great responses, I'll post back here with an update (some weeks from now.. Christmas is going to be nerve-wracking unless Big Company really just wants to get this done before the end of the tax year).
Having gone through acquisitions myself, I've learned that BigCo tax issues are entirely different than YourCo tax issues - i.e. they're going to think about taxes (cap gains, operating taxes, etc.) with different rules than you will.
Are they buying you just to get you out of the way? Is that ok with you?