Ask HN: Selling my first company - need help with the process

I built a product which company x is willing to acquire/license. From my estimations, they will be adding at least $*M to their bottom line. Company x also agreed that my estimations are reasonable and accurate. It is really glad that most arduous initial part of the initiation/demo are all done and both of us are completely upbeat about the deal. For a lot of reasons, I prefer selling out instead of releasing it to market myself - unless deal falls apart. I haven't raised any money so far.

Now, I need help in some best practices going forward. Things like, 1. how do I come up with price tag for my product(I don't want to have them low ball or I don't want to ask really high number either). 2. what is involved wrt legal paper work.

anything else i should watch out for in this time frame

thanks

PS: I am a regular user and contributor - I am using throwaway login just to be anonymous.