course backups info

Hello team,

I have to do course backups of an entire moodle system to import all of the courses in a our LMS. This Moodle LMS is not new, so I would like to speak bout various aspects:

1 Some of the users could be in both systems so, Should I make the username unique making an username update to do the username same as the user email?

2 Can I bring into the backup file the course custom fields and user custom fields?

3 Some of the courses are designed with different languages. Is in the course backup file the languages to import it in the new LMS too?

Thanks