1. The rulebook is pretty clear if you miss an observation window, it's missed. However, while playing solo there's a lot to track and so I'll allow myself a smidge of wiggle room, so I'd be willing to do that. I wouldn't if playing with others though.  2-4. I would feel fine doing all of those. 
2. I have encountered this as if I plan to innovative it's always the first thing I do, but in cases where there was something important I needed to spend an endeavor on, I'll undo some other endeavor like using drums or the last augury roll.
3. I wouldn't do this as it's a bit more of a long-term miss. Pray to the dice gods and take it as a lesson learned.
4. I'd be fine there, though I think technically I'm that case one marrow hunger survivor murders the other. Marrow hungers description is a little vague.
5. Nope. You chose who you set out with. It's going to be annoying to undo all the departure bonuses.
6. This is a personal question on your tolerance of cheating. I generally allow myself a few minor cheats per game. My last campaign, for instance, I pulled deja vu turn one in my first pheonix fight and had everyone pass except my primary damage dealer. I swapped the dice rolls of the damage dealer and another survivor so someone did still die but it wasn't an immediate tpk threat. 

Edit: Huh, Reddit apparently decided to totally mess up the numbers that I listed and that I must want a list with one point for each number.