Question 1. There's some solid state voltage regulators that don't need that "suppressor". I bought one from rt-eng and it had 3 posts and it pulsed 5 volts like the originals. I bought another one (different cluster) from, I believe Van's Auto, it only had 2 posts and was a constant (not pulsed) 5 volts out. It even came with documentation saying the "suppressor" is not needed.
Question 3. I looked in my 1970 Barracuda service manual and it showed the clock wire for a Standard dash as black and for a Rallye dash as grey. I assume Challengers would be the same. Careful not to confuse it with the tach wire which is grey with a tracer.
Question 2. Still investigating.