1) I actually applied STEK to the hood of a C7 a few weeks ago and its a very good looking film...it was actually a hair smoother than the Suntek it was replacing. I have it on the deck lid of my wife`s car too and the hydrophobics are impressive so far. That being said I haven`t been able to see how it will hold up long term yet and I would still apply an actual coating regardless.
2) I feel all PPF needs some sort of added protection, whether its a wax/ sealant, or coating. I applied lots of different coatings both pro and consumer grade to self-healing films and I`ve never seen any negative effects from it. I have heard a few others say these 5+ layer coatings can diminish it, but I`ve not seen it myself...probably because I don`t use those coatings.
3) Haven`t tested this myself
4) You will see a little difference just having the film applied (in some cases the film looks better) but as far as coating I think any visible difference would be minimal but it depends on the color of the car and coating used. Regardless, I would coat both the paint and film as the film is still susceptible to staining IMO.
5) in 2-3 years if you decide to recoat the film I would wash the car, decon, clay, and a very light polish just to clean and "scuff" the surface.
6) Light marring should self-heal. Surface scuffs can vary greatly so it`s hard to say. You can polish lightly but it should be kept to a minimum. Aggressive polish can remove the top coat and your self-healing ability.
7) Maintain it like you do the paint.
I think you`d be very happy with STEK film, but Suntek, Xpel, and 3M are all very good too.