You don't watch Marin much, do you? He's nearly always nervous at the start of the match then slowly settles in and starts serving better. Nadal, Kyle Edmund and Fed all got their chances at the start but Nadal and Fed took advantage while Kyle unsurprisingly didn't.
It was not just serves, his baseline shots were flying long in the first set.
No one says that first set would not go to Federer either way, however what's different is why it happens and how one is emotionally and psychologically prepared for the scenario. Really easy if you put yourself in his shoes. Racquet feels different, you're not feeling it, balls go long, serve is not working, and you know you're beating yourself because you don't feel the racquet well. It's not the same as usual entering slower into the match,
We know Marin, but he was riding at a higher confidence during this AO than usual, and he was playing much better tennis at the tournament than his average. Both was connected, he felt good because he was playing well. I personally thought he had a good chance in finals match this time as his game was strong. Inside outs he was making throughout the tournaments were insanely good, from both wings. It's not his standard game, it was significantly better and represented a big weapon for the finals.
However Marin didn't react well to BH slices on his serving games, once Federer started to do it (in the middle of the third set I think). In pressure to keep initiative and attacking he presented Roger with some easy points by BH UEs, which cost him being broken twice and directly losing a third set. So if topspin baseline game eventually went Marin's way, even under circumstances how they went, I'm not sure would it be any different in a 'normal' match. Marin has something to work on if he trully wishes to make one additional step in quality. Not impossible, Federer is making his full technical and tactical potential from last year, so it's quite possible for Marin to step up in quality regarding few elements. Includingh his serve. The deicision to take more time and not rush it, I think it's grear for him. Teaches him patience and it might help him raise his first serve in %.
That's not unprofessional, that's being supestitious. Many tennis players fall into that category.
I don't think he'd chose outdoor if decision was made early, but we cannot know for sure. Would be insane. However in circumstances Marin mentioned routine for this AO being the reason for picking outdoors prep, however it might be superstition as well being decisive to pick outdoors in given circumstances, sounds quite possible.
Absolutely. If the match had been played outdoors and Federer had won we'd all now be hearing how the roof should have been closed and the fact it wasn't was obviously designed to help him.
Except there wouldn't be any good argument to support this.