For the most part, yes. There are some differences between the dlx and the sr5 models as far as the door panels. Also, some doors have a wing window and others have a full window. But they will all mount and fit to the bodies. I believe the 2nd gen toyota trucks are the same also.
Yup. I've converted doors from full length glass to wing window setups, no reason you couldn't go the other way. If the door you're using wasn't electric, you'll have to drill out a hole to pass your harness through, and the side window mounts are in different locations depending on whether the door had a wing window or not. But everything is basically compatible.
They're the same, they all even have the place for the 2nd spot for the rear passenger door release on the passenger side. Everything is interchangeable.
Yes. But you have to replace the window regulator assy too, not just the glass (if I remember correctly). That mechanical assy that holds the glass and raises/lowers it is different between full window and the smaller window that how's with the wing window. The door shell is the same for trucks/ 4runners 2WD/4WD.