I sincerely feel your pain, we also had to fight old paper and excel habits with a digital tool. I am also in a startup working on a Scheduling product with math optimizations (absence management, work constraints, IBM Cplex solver)...! I will be happy to review your open source code and see if anything can be reused on our side. PetalMD has a freemium approach in a niche market (Canadian healthcare providers), and we burned lots of money before we finally focused on the core value for our user base. The freemium gave us the critical mass and leverage to have discussions with partners and we learned through the years what had to be enhanced in our product to offer several pricing plans.

Our niche is really helping focusing the product enhancements and the marketing efforts. Scheduling needs are broad and we constantly have to refuse opportunities.

Good luck with your next venture!