Hello And Welcome!
No luck with the wiring, but with the tint:
Yes tint helps, but you would need to keep the level of transperency within the legal limit.
Here in India, its 70% for the front and back wind-screens, and 50% for the side windows.
That is to say that the front and back wind-screens need to let 70% of the light to pass through.
So mebbe you can Google you local transport authority regulations and see how far you can go.
You would also be well advised to keep in mind that tinting will reduce visibilty, especially through the front and back, so it will take sometime to adjust to, and you will have to be careful, especially at night, when you are in danger of not noticing a vehicle that is approaching you from behind.
About the actual work, it is best left to the experts, but there are 2 things you will have to careful about.
1. if you have a defrost element in the rear wind-screen, ensure that an overzealous tinter does not use the blade on it and snip off the connections( happened with me, even as i was reaching out to stop him. had to get a whole new wind-screen)
2. The door-cards need to be taken off, so that the tint reaches down, below the level of the place where the rubber beading reaches, so that it does not start peeling away due to a constant tug at the very bottom edge, when you roll the window up or down.
That said, you could also take off the inner roofing and install a heat insulator and put the upholstery back. this would discourage some of the heat from permeating into the cab..
Lemme know how it goes......
Cheers.