In my opinion, it's a easy-intermediate level task.
Almost guarenteed... you will screw up your 1st, 2nd, or 3rd sheet.
Pick a day that's calm. No winds, no dust blowning around. wash all your windows, scrap clean with a razor blade. Use the razor blade, because no amount of towels and alcohol or soap will remove the little tiny particles or lint that stick to the glass that you can't see.
Handle the film with care, and read the directions that come in the box or roll. Especially with the protective backing on the adhesive side removed, any mishandling will cause creases and screw up your sheet of tint.
If you are doing the rear window of a zx3 or zx5, I'd recommend removing the plastic trim. This will give you more room to make clean cuts. Also the rear glass is curved, so you have to apply the tint film in strips. Your other solution is to use a heat gun set on low temperature, and form the tint to curve... Otherwise bubbles will appear.
you'll see some lines beside the defroster lines, but they go away with time. The water will evaporate.
Since you have a sedan, I think the rear window might be tricky.
also I have little experience with roll down windows... I tried one time and failed miserably. If I were to give it a second try, I would remove the door panel so I'd have more area to work with. Also once the door panel is removed... The glass comes out by removing 2 bolts. Removing the glass might make it easier...
But after all that work, you would have probably rather spent the $150-$200 and got it done professionally.