Definitely quite a unique position compared to the common rewrite story. Small company, long-term rewrite timeline, small rewrite team, able to influence the sales activity and deployment. I think these constraints are important to your success (and fun factor), but I don't have the complete picture. I'm really welcome to any points against what I wrote above; currently I'm intrigued on reading on how software projects works or doesn't work in real life and your story is really interesting.