Turn off iCloud sync to switch to OneDrive

I've been using iCloud Drive to back up my files (documents/desktop only) on my work laptop. However, I'm close to running out of space and have 1 TB of OneDrive through my organization, so I'd like to switch to that for backup. I'm being prompted to turn off iCloud sync to turn on OneDrive. I have two questions really -

a) is there a way I can do this without turning off iCloud Sync, at least until I turn on OneDrive, or

b) if not, what will happen to my files if I turn off iCloud sync and choose to keep a copy? Will the copies stay where they are in my documents folder?