For the Z axis motor you may want to stick with a 1.8 degree motor and choose a lead screw with a finer lead, for example 2mm. That can give you more torque and holding power for a heavy bed that moves in Z and still gives a very high Z axis resolution.
Also, if you're only using 1 motor for Z, is it a cantilevered bed, or is it a single motor belted to the lead screws?
steps per mm formulas:
xy_steps_per_mm = (motor_steps_per_rev ∗ driver_microstep) / (belt_pitch ∗ pulley_number_of_teeth)
Z_steps_per_mm = (motor_steps_per_rev * driver_microstep) / screw_lead
e_steps_per_mm = (motor_steps_per_rev * driver_microstep) * (big_gear_teeth / small_gear_teeth) / (hob_effective_diameter * pi)
BlTouch: https://duet3d.dozuki.com/Wiki/Connecting_a_Z_probe#Section_BLTouch
If you're new to RRF I suggest going with RRF3 to start with.
You can get a basic config here: https://configtool.reprapfirmware.org/Start