So for the capsule, you’d set the capsule half height to half of your desired character height. In this case it’s 87.5 cm.
Then since the camera is the parent to the skeletal mesh component arms, you can just raise/lower it to where you want the eye height to be. The gun attaches to the skeletal mesh, so that should always be the proper height. However the only caveat is if the 3D arms are too long/short for your new height it get’s less intuitive on how to adjust that. (just changing their scale skews shape and animation so that’s a no go).