By purchasing you agree to the Chisel license & terms. All sales are final; see terms for details.
Windows is the primary platform and the only one that has been thoroughly tested. Linux and Mac are not the current focus. The engine may run on those platforms but they have not been tested and should not be assumed to work.
C#. You'll work in Visual Studio with the provided SDK projects.
Yes. No royalties, no fees, no restrictions on what you build or sell with it.
No. You pay once and own it permanently, including all future updates within that major version. Future major versions are sold separately.
All sales are final once the source code has been accessed. If you're unsure, ask first.
Check the documentation, it covers every major system in detail.