The mod is installed via CMM which you can find in PA in the latest test version (PTE) of the game. The proper install instructions can be found in one of our older moddb articles "Legion Expansion (Public-Beta)". I am not 100% sure exactly what the mod size is as of the current version, but all the required files together should be about 80mb (Due to the fact that the download is a zip file).
EDIT:
I'll make sure in future articles to have the install instructions easily accessible.
Nicb1
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