The more you do yourself the more you control the outcome. You also preserve options like filling in the rear window and adding scoops or other body modes.
In the end if it's about saving time. Well.......... the window openings and fitting doors are really a very little amount of time compared to the overall build. Again you might want to add stiffing plates to the door mount area in the body or take a different path with the door shock system as others have.
My advice would be to get the car home and spend some time thinking, reviewing others builds, make a few phone calls to the rest of us. Start with the mechanical systems to get your feet wet while you get acquainted with the bodywork questions.
Begin with an aligned chassis and suspension system at the correct ride height on the car before you put the body on. It also helps if most of the weight is in the car to see how the wheels and tires fit in the body as you put the bodywork on.
None of this requires any "advanced" skills. You won't need to classes to do this. It will be a learning process but that's a big part of the fun...............at least for me.
By the way you are welcome to call me any time. Just drop me a PM and I'll send you my Ph#. I am sure many others will be happy to also help as well as RCR.
Take your time, enjoy you're new hobby and have fun.