How Much Disk Space Do I Need?
Plan for roughly twice the size of your export while it runs, and less once it is done.
You need room for the zip files, room for the unpacked photos, and room for the organized copy. That is why twice the export size is the safe number while the work is in progress.
Converting HEIC to JPG adds a little, because JPG is larger. Converting videos can go either way depending on the original format.
Takeout JSON Metadata Fixer checks the free space before it starts and tells you if it will not fit, rather than stopping halfway through. It runs on your own computer and is free for your first 500 photos.