I've been plying Sellswords for a few years now, so this is MY understanding of the rules, if asked Andrea may have a different opinion.
1. The rules state "apply the effects of the cards one at a time, in the order they were drawn" so yes, you apply each card, including reshuffles, before drawing the next.
2. Some scenarios state a table edge you should (or should not) leave by, if it is not specified then leave by any edge.
3. A shield roll is at the unmodified DL of the foe.
4. Just one, the rules say "an Activation die".
5. Yes, you can use Whirlwind without having to move first, if you are already in contact then the foe is certainly within 4".
6. Quick reflexes says +2 to dodge rolls, nothing to say that excludes traps, so yes you can.
7. The improved DL only applies when the foe is shot at, not when shooting at you.
8. Yes, the bonus move to the closest minion or horde is a part of the bosses activation, then the minion would get their own activation from the Monster Frenzy.
I hope this helps (and makes sense). These are a great set of rules and my go-to for all kinds of things! Enjoy playing them.