1) No idea. I'm not sure anyone can answer that, because most people don't have two of the same car to do side by side comparisons ;)
2) Look at the respective web sites for those companies and look at the tint specifications. Take a look at this link from Solar Gard to see what the minimum you should expect to see in tint specs. There is a lot more to it than that, but they've dumbed it down for car owners for some reason. They also have a glossary if you don't understand what the specs mean - which is where you can see what would typically be included in home or commerical tint.
3) It sounds plausable what he's saying. Tint film goes on the inside surface of the glass, and tint can reject (reflect) the heat energy. This means not only do you have the sun blaring down on the glass and passing through from the top, but then it's being reflected back up from the bottom to add even more heat. Plus the hot air in the car is rising etc. But I would wonder "why only the sunroof and not any other of the windows"
4) Here is something I can tell you for sure. If someone tells you that they don't like tinting the rear hatch glass "because it's too hard", then run as fast as you can. What they really mean is "my tint skillz are crap and I'm not good enough to successfully tint the rear hatch". So go to someone who DOES have the skills to do it properly.
5) Maybe yes or no... whether it's covered by "warranty" isn't actually relevant. The dealer's subcontractor damaged the car, so make the dealer take responsibility and resolve the issue - even if they have to pay for the parts. It's certainly not your issue.
6) For two windows? I would say about $120 based on Sydney prices... but a fair price in WA is whatever you can get it for. Obviously the dealer is car more expensive than a third party, cause they're adding their margin on top. If you really want to know what the going price is, start calling the "Motor One" dealers and ask, since Tint-a-car already let you know that they're the ones the dealer use to put on "Street legal".
As for boot liners... look in the accessories thread :)