Answer 1

Given a total different computer processor and a completely new OS, your first step would be to make a cross compiler to generate binary for that processor that runs on some existing system. Then, you would write the OS there and download the binary to your target similar to how Android apps are written on PCs. Once you have enough of the OS working, you compile the cross complier for the new processor and download it. From then on, you can develop on your target system.