Front caliper types

Initially the brake light on my instument cluster is always on. Upon reading in the manual there are three things that can cause this, 1) parking brake on, 2) low fluid in reseviour 3) an imbalance in pressure from front right to left
I have a reseviour sensor and a sensor at the master cyliner itself
76 300D w115
Upon further investigation under the car I found that I have a 60mm Teves (ATE?) caliper on the right front and A 57mm Teves on the left. The car pulls right on braking. i am assuming this is causing my problems.

1) I will replace one to make them the same as required by the MB manual
2) Is 60 better than 57?
2) do they all use the same pads?

I plan to replace lines, pads, cylinder repair kit rotors etc
Also my cruise will accel but not hold does this light have any effect on cruise?
Thanks