1) If the damage was caused by the snap, then why did it started (and ended) before the actual snap?
2) How could he get damage of the power of something that didn't even happen yet?
3) Of course the Stones went crazy of him: they were the ones responsable for hia burns!
4) Which means, once again, that some time before tha snap and after he put the Gauntlet on he tried to bring her back. Tell me, why would the Soul Stone allow to bring back Nat or, depending of which one we are talking avout, Gamora? Especially after it was made clear that is impossible.
5) Yup. I personally do believe that Hulk would have won if he was in Thanos place. Especially that from the moment the gist fight from the beginning of the movie ended and till the battle with the Guardians and Avengers started there wasn't even too much fight.
6) Iron Man repeatedly punched Hulk in the face, about twice per second, with the Hulkbuster, which seems to be stronger than a jackhammer, before throwing a building on him. Hulk didn't got any scratch. You can also argua that the Power Stone was making Thanos more resistant, like in the comics, but this I must admit that is pure speculation.