First production motorcycle with a hydraulic disk brake would be the Honda CB 750 in 1969
Ducati 600SL and TL Pantah in 1981
You use both front and back brake for braking.
The front one.
Shift your weight forward while applying the front brake.
Yes
Front brake head check side strid
If you are going over 10 mph it can start to get very dangerous because most of the stopping force applied to a motorcycle is from the front brake (estimated 70%). The back brake can lock up easily.
Hydraulic , front disc , rear drum , with rear ABS
Over 20 mph, front brake then add back brake. Under 20mph a little front but mostly back brake. Under 5 mph back brake only. In an emergency front brake hard and add back brake hard. Change down after braking, even if you brake to a standstill.
The rear brake pedal is under your foot on the right hand side and the front brake is a lever on your handle grip on the right hand side.
If there is a hydraulic master cylinder at the clutch lever (looks like the front brake) then...NO.
To send more pressure to the front wheels, where it is needed.