No problem. I see that I didn't understand your initial question. You want to interpolate between waypoints.
A Path2D would be best if you want to easily implement a curve inside the editor, and you would get smoother rotation if you create a curve.
If it was to be done in code, then interpolation between two way points will give you the distance, based on some alpha value (0 to 100%).
The rotation can be calculated by using the angle of that difference vector. Then atan2(y,x) or vector.angle() should give you the angle towards the next waypoint. Adding and offset of PI in many cases, to orient the sprite to face along that path.
var difference = B - A
var alpha = .5 # Some distance between 0 and 1
var new_waypoint = A + difference * alpha
var new_angle = difference.angle() + PI