How to paint hair with alpha/cutout



I am 3d artist but I am new to painting/texturing (always worked with the team).
I am painting the low-poly hair in substance, I want to keep only the area I paint rest should be transparent, I don’t know how to do that.
If you are willing to help please explain the steps as I am a super newbie :frowning:
Sharing the screenshot:

Secondly where my hair (two objects) overlapping, it’s creating the darker weird blackish shading, would it be shown to end results ?
Sharing the screenshot:

Best Regards,