BMG Extruder upgrade questions

[dore_m]

Sorry for my ignorance here. Hope someone can help.

I use my 3D printer occasionally, so I have to re-learn many things when I upgrade or make changes. I currently have a Geeetech "Prusa I3 X" and am upgrading to a BMG extruder - so I'm moving from a direct drive to a 3:1 gear ratio. In printing carriage parts, I've had to flip the drive belt, so I also need to change the direction of the X motor.

I'm always a bit confused which settings I change using the Arduino configuration.h file, what I change in the Slicer, and what I change in the software settings. I currently use Repetier-Host with Prusa slicer.

So with this basic confusion, where do I change:

1. The new settings for the BMG extruder (extrusion ratio/speed), XY offsets (from the endstops) for the new nozzle location?
*edit: I think I found the Extuder E-step value:
#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 2560, 415 } in configuration.h - 415 is for BMG.

2. Change the direction of the X motor?

Thanks for the help. Or if you can point me to the right resource - that would be great.