If the course is as huge as you say, once you have installed the localhost Moodle, you will need information here https://docs.moodle.org/22/en/File_upload_size to change the upload file size. It is not difficult, but you need to be precise about making *all* the changes.
The next step is Site administration > Courses > Restore course > drop the .mbz and follow directions. Be very careful to choose a category (Miscellaneous exists by default) or you'll restore the course to the site's front page (I've done this), which causes lots of trouble.
Note that your localhost Moodle will run much slower than the production server you are used to. Be patient.