Same as any other command line copy program. You'd probably get some overlap depending on how you run things.
Same as above. You can over run things.
It really depends on specifically what you are running and what you'd want to happen. Generally, if you are copying something, it depends on who gets there first as that's generally the issue with any copy program unless there is some file locks or a higher level of conflict control.
Rclone copy is going to be like your standard Windows/Linux copy command though so what you'd expect to happen with those, it would be the same thing.