A dual boot system is not a big problem as long as you boot in EFI mode and use GPT partitions. I have been running a dual boot system (Windows 10 and Arch Linux) for years without any problems.
You should allocate around 500 MB for the EFI partition. This allows you to install Windows and a Linux distribution and still have reserves if you want to install additional Linux kernels, for example.
If you want to change partitions, first make a data backup on another data medium. Because something can always go wrong. Even if it’s just a power failure.