I'm trying to transfer large files from 1 drive to another (win10) and it gives me this message:
Do you want to restore to same drive. This can reduce the chance of a successful recovery.
does this mean I will lose all my files I lost that I've used recuva to find..over 300K files or will I lose my current files on any drives I'm trying to transfer to other drives to make room for the large 300K+ files I've recovered using recuva
It is saying that you have requested the recovery to be made to the same drive holding the deleted files. If this is done then the recovered files may overwrite the deleted files that you are attempting to recover, hence the warning. For such a large amount of files you should be recovering to a separate partition.
Your third sentence made my brain hurt but Recuva will not delete or overwrite any live files on any partition whatever you do.