While I personally can't help you. Someone has already made a similar mod, so you could either study his mod files or post a comment on his mod page.
Here's the link:
Weight and Level Cap mod by Gid25
https://www.nexusmods.com/divinityoriginalsin2/mods/23/? EDIT: Apparently that mod has some problems, but fortunately there is another similar mod:
https://www.nexusmods.com/divinityoriginalsin2/mods/131/? 
