I am looking into using a 4N32 opto-isolator and am struggling to find information on its pin 6. This looks to be the base of the transistor (darlington). I see example circuits where they appear to leave this pin floating. I am curious to know if I should make a pulldown resistor connection. Anyone have any advise or insight as to what I should do. What pull-down resistance to use.
Normally you would leave it floating. Adding a resistor to the emitter can speed up the isolator somewhat, at the expense of CTR.
You wouldn't (or shouldn't) be using a Darlington optoisolator if you cared about speed, but if you want to give it a try, something in the 100's of K ohms would be a starting point.