For master rule 4, why can't I occupy two extra monster zone?
For balance reasons, Konami introduced a special rule for the second extra monster zone.
It is possible to occupy both, but only under certain circumstances. Just having a link monster point there is insufficient.
To occupy the second extra zone you need what is called an extra link. This means having monsters co-linked from one extra monster zone all the way to the other.
You can find this illustrated here:
https://yugioh.fandom.com/wiki/Extra_Link