Hard to say when it comes to the first question.
For the second, dutasteride 0.1mg/day did have better efficacy than finasteride 1mg/day https://www.jaad.org/article/S0190-9622(13)01171-7/abstract
As for the third, I don't know, but in the '06 study they showed that dutasteride provided a roughly threefold higher...
Dutasteride Dose (mg) and Reduction of Scalp DHT (%) https://www.sciencedirect.com/science/article/abs/pii/S0190962206012874
0.05
~ -20
0.1
~ -35
0.25
~ -45
0.5
~ -50
1
~ -55
1.5
~ -65
2
~ -70
2.5
~ -80
As for serum DHT, I don't have the data, but from memory it was ~95-96%...