So do all the skills need to be put into slots to work? - The Witcher 3: Wild Hunt
For The Witcher 3: Wild Hunt on the PlayStation 4, a GameFAQs message board topic titled "So do all the skills need to be put into slots to work?".
Upgrades | The Witcher 3 Wiki
The Witcher 3: Wild Hunt horse guide tells you all you need to know about your mount, and where to find and buy upgrades for inventory slots.
How To Get More Ability Slots With Mutations In The Witcher 3
The following guide will tell you how to get more ability slots using Mutagens for Geralt in The Witcher 3: Wild Hunt.