What hanger are you building? You can buy one if you can’t make your own.
1) 3X20 min of manual stretching?? This is too much.
Hanging use light force over a long period of time. But manual stretching use more force for short time. I don’t know how much force you can produce by your hands. But you can easily produce 25 lbs (you can produce a lot more). So if you apply this force for that long time, you’ll pull your penis off. And I don’t think that any one can stretch for that long; your hand will be tired, and you’ll not be able to grap your penis. So you can use hanger to produce just the appropriate amount of force, and use it without bother your hands.
2) I think it’s better to do it all at once. Because when hanging, you need to reach fatigue. And you need at least two or more sets to reach it (depending on the weights and time of the set). And you can’t reach this fatigue when you split your routine. But you may still have some progress if you split your routine, but I think it’s more beneficial to do it all at once.