Best way to get windows onto my new build?

Finally bought all my parts for a new build into my old case, but this is my first time building myself, having always used something like pcspecialist before. I’m feeling fairly confident(for now!) and read up and watched plenty. My last query though is windows.

What’s the best way to get it onto the new build. I my current setup has a 1tb SSD which windows is installed to and a 1tb M2. I hadn’t planned on keeping the SSD, but was going to keep the M2 for additional storage like photos, music etc. though I don’t suppose there’s any disadvantage to keeping the SSD as well?

Would reformatting both and just moving them to the new build be fine for a hassle free way to get windows up and ready on the new build? Or would it be better doing a fresh install using a usb?

Further, if I did just move the current hd’s across, can windows then be easily transferred across to the new and much faster 4tb M2 I’ve got?