Footsteps are one thing. Place them with Niagara and control them that way.
Walls are another.
Create a material function. Add an input as material attributes. Break the material attributes. Play with the settings - to create the fade however you want/what fits gameplay.
output to material attributes.
In the material, make material attributes with the wall stuff. Put the function in and connect it. Connect it to the output (after checking the box to use material attributes in the material settings).
Then you just create a dynamic material instance, and from it. You can adjust the scalar parameter that controls the fade over time.
as far as material process you could also build the fade into the material using time node, but this is prone to reset, so stick to managing it with a timeline in the blueprint. At least you are sure it can only ever trigger once per wall.
Don’t forget that you also need to remove collision.