Inventory and weakness... (Horizon: Zero Dawn)

1. Guys , is it possible to increase the size of the inventory?
2. Just can not understand how to operate the weakness of some monsters. For example , pilosula weakness of the body to the fire. Vusmert pumped to fire a bow shot in the body or are highlighted under the belly crap. And no matter the damage anyway only 5% of his health. Cho for x...???