Actually, a reset would do, even keeping your files: http://www.laptopmag.com/articles/reset-windows-10-pc
But, if you own a OEM copy of WIN you need to buy a new license. Only Retail versions allow switching motherboards.
To avoid a conflict with drivers, yes. Although I'd call it formatting your drives rather than reinstalling Windows, as that comes after the format of your HDD/SSD.
Actually, a reset would do, even keeping your files: http://www.laptopmag.com/articles/reset-windows-10-pc
But, if you own a OEM copy of WIN you need to buy a new license. Only Retail versions allow switching motherboards.