I can't answer all your questions, but a few at least. You should use the latest kernel (and firmware) and Mesa you can. That will give you amdgpu (kernel drive

I can't answer all your questions, but a few at least. You should use the latest kernel (and firmware) and Mesa you can. That will give you amdgpu (kernel driver) and radv (user Vulkan driver) from Mesa and the best compatibility and performance. AMD's proprietary driver, amdgpu pro, sometimes performs better, but the consensus these days is to just stick to Mesa and open source.