To use RedKit, you have to have the latest Next-Gen version of W3 installed.

Prepare aboutt ~70GB of space on top of your game installation, so about ~125GB total.

No, you can’t get around it with RedKit.

Download RedKit from Steam, GOG, or somewhere else.

Launch and just follow RedKit installation instructions.

Step by step:

1. Have latest Next-Game version of Witcher 3 installed
2. (optional) remove your mods & custom DLCs if you had them installed.
3. Download & launch RedKit.
4. Follow installation instructions.
5. When prompted to choose a folder for Depot, preferably, keep to a short path
   1. Keep it short to avoid reaching Windows character limit for file paths.
6. Let RedKit finish generating a Depot
   1. usually takes 40+ minutes, up to 3 hours - depends on your machine
7. Done