Hello! I’m not sure I understand your question but here is a clear up. You enter the VOR at a designated radial, no waypoints (unless you want), and leave at a designated radial. I fly IFR a lot with VORs and I don’t use an fpl, I just use VOR’s by, as said before, entering the at a radial, and leaving at a radial.
VOR navigation is best if you’re able to hop from VOR to VOR without any intermediate waypoints in between. This answer will merge into question #3 you had and that is do you need to fly an airway. Although not required in Infinite Flight, its not a bad idea. The fact that you’re familiar with the term airway is more than what most people know so it wouldn’t hurt by doing so. Kuddos to you!
These fixes are not necessary. These fixes such as DXX.X VOR are procedure fixes. Because we don’t have a way to hide High, Low or even differenitiate procedure fixes, all fixes are seen in our map. These fixes which start with D followed by some numbers are generally on an arc or other instrument approach that utilizes distance to plot a point on the map to give the pilot a point of reference.
The AP will fly a VOR course if you have a course and a VOR set. So yes, it is realistic to engage VNAV. Keep in mind of your CDI (Course Deviation Needle) when doing so. The AP will fly in the direction of whichever way the arrow is pointing. not referring to the to/from flag