A few questions regarding the game rules

I bought Red November a few days ago. After a few trial games, I have the following questions regarding the game rules:
1. Is it allowed to have more than 1 gnome starting the game at the same room?
2. After opening a hatch, water from high-flood room should flow to its adjacent no-flood room. But what should the consequence between a high-flood and low-flood room? No change?
3. Regarding spread of fire, if there's no room for spreading (e.g. flooded rooms/ rooms already on fire), should it be "no effect" or there should still be an increase in the Asphyxiation track?
4. On trading items between gnomes, is it necessary to be a fair trade (i.e. 1 for 1, 2 for 2...)? Or it can be 1 for 2, 2 for 3, etc.?
5. On timed destructions, if two of the same timed destruction tokens (e.g. missile launch) are activated, can they be resolved by a single successful fix-it action?
Sorry for posting so many questions. Hope any expert of this game can share your views.
Thank you very much!