Howard is right on ... something to consider in backing up as well as restoring with moosh.
Get organized first ... by that I mean, compare categories in moodle servers from which the courses will come to the destination moodle ... get the categories worked out on destination server.
In servers where courses are to be moved, use the backup.php script in a looping bash shell script consisting of nothing but the course id's of one category of courses to be moved.
Example: from moodle A has a category for basketweaving with 10 courses in it ... id's 45, 79, 323, 555, 679, etc. Use admin/cli/backup.php with a destination of 'mabw' destination directory and backup just those id's to that manually created 'mabw' directory.
After transferring the 'mabw' directory to destination server where you will moosh, much easier to script a moosh command to restore all courses in the 'mabw' directory to the category desired on destination server.
Did something similar and due to naming of backup files, at first, had a heck of time looking at backup filenames and getting them restored in the 'right' categories on destination server.
And another thought/consideration ... conflicting users ... accounts plus roles. If from Moodle A user had admin levels, do you also want same user to have admin levels on destination Moodle?
Easy restores if the backups were no user.
Now I have a question ... it might change approach ... what is the expectations in what you are calling 'for maintenance reasons' after the courses are on destination server? Archival? All users to access courses on the destination moodle server after xfer? Edits to courses on destination moodle will show in moodles from which they came 'automagically'?