Answer 1

Assembly language is essential; another supplementary high level language such as C is strongly recommended.

Target what processor platform your operating system will support. IA-32, ARM, and x86_64 are the most common for personal computers so they're your best bet.

Decide if you would rather do it all yourself from the ground up, or if there is an existing kernel you would like to build on top of. Linux from scratch is a project for those that would like to build their own Linux distro.

Decide if you're going to use your own boot-loader or a pre-created one such as Grand Unified Bootloader (GRUB). Since coding your own bootloader will require extensive knowledge of the hardware and the BIOS, it may push back the schedule for programming of the actual kernel.

Only if you're willing to learn a lot. You will require a full understanding of at least assembly code, and the motivation to learn more. Building your own OS is not a small task.