honestly it would be easier to backup all of those drives and reformat the drive to ext4 or btrfs, then put them back. but only easier if you have access to storage that can fit all of those games
biggest problem with lots of games on multiple ntfs drives and 1 supported filesystem is that you might run out of space on the supported filesystem from all the prefixes
username really is optional at this point. I still usually recommend it just in case, but nowadays I haven't seen issues related to it. edit: It's also not really harmful in any way to use deck as a username