Maintaining a wall around the window

[jt3000]

Hello!

I am a novice when it comes to applying work with interior decoration and I need advice based on these pictures.

My questions are:

1.
What type of tool is needed to remove the old paint that is starting to crumble (the gray paint)?

2.
After removing the old paint (gray paint), what is the next step?

3.
Do you need to fill the various cracks first, or is there another preparatory work that needs to be done?

Thanks in advance!