First thing. Post you location in your profile!!!!!!
It's now so much in what order you do things you will take it apart many times as you go forward. Having said that keep in mind that the car you build will be something that you will need to maintain for many years. Think a lot about how you will be able to work on it later. Things like nuts located deep behind the bodywork where you can't reach it without taking everything apart should have a nut plate installed instead of simply putting a nut on the backside of a panel.
Or where to locate large components like fuel pumps. Put it where it not only will work correctly but where you can get it out of the car without taking the body off or apart.
Generally speaking I would say to assemble the big stuff first. Put the power train in the car with the suspension, exhaust system, steering, fuel tank, radiator, AC big parts, interior big parts (seats, steering wheel, peddle box, and shifter) then complete their systems one at a time like the cooling system big plumbing, then the brake system tubing, fuel system parts and their tubing and hoses and the other mechanical systems first before you go on to the electrical systems.
Once you have the car put together (all the big stuff is in less electrical) do a alinement of the suspension and trial fit of the body parts and get a feeling for what your questions will be. Do the headlight and tail light mounting systems but wait on wiring for now with the exception of connector clearance on the back of the lights themselves.
Body: The windshield will determine the location of the center section and NOT the other way around along with the front and rear wheel arches and tire clearances. You need the final wheels and tires for this. The door fit will come next in order of importance after the DRY windshield fit/ center body section placement and their relative relationship to the front and rear body sections as related to wheel arch tire clearances.
Do whatever it takes to be able to DRY fit the windshield without ANY deformation of it. NONE NONE NONE!!!!! Make the center section mounting method repeatable in respect to being able to take it off the car and put in back on and then dry refit the windshield perfectly a couple of times.
Now you have a center section that can be removed and put back and the windshield will fit every time. This is a big deal but not a hugely difficult thing to do from a technical standpoint. Just a bit of patience and a lot of trial and error. The doors are the same process, patience and trail and error.
Lastly on the body. Overall it goes like this, the center section goes on with the windshield fitting in the recess near perfectly, then see where you are with the front and rear wheel arch locations and the tires. Now go on to the doors and trail and error the total pieces fitting at the same time not disturbing the windshield fit. What every you did to the body parts to get to this point is the shape of the parts but not the surface finish part of the work. You can do that now or at the end of the build. I sanded the body and did the majority of the body surface prep at this point and got the car in a 80-90% finish with all of the mounting points and hardware location and selection done and spray can sand able primer coated.
Now you can take the body off and complete the car systems do electrical and get it to the go cart stage. Once it runs (large R) and the systems check out the body can be final trial fit and finished for paint, removed again for paint and put back together for the last time. Now final fit the windshield. It should drop right in at this point.
You can see why I insist on all that fitting and checking the windshield throughout the process. It didn't fit now you would REALLY be fucked. It CANNOT be made to fit. It will not flex period.
Hey...……..your done! congrats!!!!
I am sure I missed something or others will have their own better ideas. Just keep asking questions and find the nearest SLC owners to buddy up to for beer drink help and new friendships.