1. It does not appear that you need that many washers for the light bracket to clear the fork race.
2. There should not be a nylock nut back of the acorn nut - a regular (thinner) nut is fine.

Method from the "old days."
1. Adjust the acorn nut and the one underneath so they are locked against each other tightly, and the caliper moves freely but does not have any significant fore-aft play.
2. When you want to center the brake put one wrench on the nut in back of the fork. Put a second (narrow) wrench on the acorn nut if moving the caliper clockwise, the other nut if moving cclockwise.
3. Move the two wrenches in unison till the brake is centered when you pull the lever a few times.