Here is what I learned on a 3000 mile cross country tour.
The front wheel indeed does most of the braking if both brakes are applied. So much so that I had soon wear patterns in the front rim. In an ideal world, I should have installed new wheel and brakes. That was not an option. So, I mostly used the rear brake and the front only if absolutely needed. That worked for the whole trip and on very fast declines above 35 MPH (I am 190+++ lbs). BTW, road debris such as sand got into the brake pads also. Yes we cleaned that often but it was an issue on my front wheel.
The back wheel brakes much less effective however I never worried about lock up.
Regarding hand signals: We were told to bike Vehicular Correct and we did. Hand signal for right turn was right arm point to the right. There was no confusion there. A big concern is signaling to cars so they do not cut you off if you go straight and they go right. This was done by going in the proper lanes instead of always far to the right. We had no accidents and few close calls.
Signaling right turn with the right arm while slowing down for a right turn is a safety issue if also going down hill. I found that to be very dangerous and found no good solution except a rather quick gesture pointing to the right and immediately get my hands back on the brakes.
BTW, cross country road surface quality is terrible in places. Taking a hand off the bars is not safe under those conditions. Really no fun.
Hope this helps.