So many questions
No you cant use the stock o2 sensor for A/F Map. Actually I never noticed there was an AF map in there, it unchecked in the parameters setting anyway.
If you are talking about using stock MAP sensor and Wideband feedback then yes you could do it, but only really use ful for NA applications.
Voltage for Greddy pressure sensor is based on pressure.
Stock pressure sensor is based on pressure.
That is why they are called pressure sensors lol
On the GReddy sensor 0.67V corresponds to 12psi of vacuum. This is about how much vacuum you'll pull when the car is idling.