Well first thing is get the proximity,
you can add a box collision around the door,
Then if the player enter the are (look for on event overlap on internet)
you can surely add a force to the door, since you already done it in physics.
But i think will be really hard measure the force to have a nice feedback,
you should consider using a simple animation
or even a simple blueprint that swing the door with different speed and spring.
Like the player is walking, so move slowly the door
player use kick or shot the door, slam the door
player run to the door, the door open quickly