I wrote a brief handbook about starting startups. While not an "employee handbook," it does contain some info about coordinating, getting team buy-in on ideas/movements, and making time to create and brainstorm as well as a no-penalties time to discuss and vent gripes. Some of the insights may be of interest to you, although it is aimed more directly at the aspiring founder or team of founders.
The first few sections you can read for free here https://satisologie.substack.com/p/rocketshipping-book-excer...