Gamma
Make sure the game is open in full screen mode.
If you open the gamma tab in the game settings, then sometimes you may find that there is not enough adjustment ability in order to set the correct brightness. You can increase or decrease the threshold for the maximum values ​​of the gamma settings. You need to open the file in a text editor. \bin\config\r4game\user_config_matrix\pc\rendering.xml
And in line <Var id="GammaValue" displayName="gamma" displayType="GAMMA;0.1;1.9;90" tags="nonLocalized"/> change values {displayType="GAMMA;0.1;1.9;90"}.
For increase brightness for example change on {displayType="GAMMA;0.5;5;225"}.
For decrease brightness for example change on {displayType="GAMMA;-4;1;250"}.
Save file and start game.

Hud offset
For hud offset you can edit user.settings file (C:\Users\{user_name}\Documents\The Witcher 3).
Experiment with parameter values uiVerticalFrameScale and uiHorizontalFrameScale. In my case:
uiVerticalFrameScale=1.05
uiHorizontalFrameScale=0.99

Alternate Axii not working
Solution from steamcommunity:
" I have managed to solve this for myself on the PC. It now works! I can have puppet and delusion at the same time.
To fix this:
Navigate to your folder: C:\Users<User Name>\Documents\The Witcher 3
Open the file "input.settings"
Find all the entries for "IK_Q=(Action=CastSignHold,State=Duration,IdleTime =0.2)"
Change the entry to have an IdleTime of 0.01. So after your change it should look like this:
"IK_Q=(Action=CastSignHold,State=Duration,IdleTime =0.01)"
There are multiple entries of this setting, so you will have to change them all.
I didn't test it with other signs as this is a universal change to all alternate sign modes. But I am just happy to be able to use puppet and delusion at the same time now. It was driving me crazy to have to choose between them."