1. I know this might not be helpful, but it really depends on your style and the situation. But here are some handy rules of thumb I use:
- Whoever speaks first goes first
- If more than one person wants to do something at the same time and those things don't conflict, have them all declare their intended actions before resolving anything
- If someone wants to wait to see the outcome of another player's action, that's totally cool, but waiting can have its own risks - look to the fiction for ideas for ways to complicate things for them
- If someone hasn't already spoken, ask them what they're doing - this can happen before or after other rolls have happened, but it's important to keep everyone involved
- The more chaotic the situation is, the more I'll jump around between people
- If two PCs are going head-to-head, always give the one who didn't speak first the chance to interfere, and once the first player's move is resolved, always give them the chance to respond with an action or move of their own as the very next thing that happens
2. Again, this is going to depend largely on the fiction. In general, the more dangerous the foe, the more often I'm going to have them act. A particularly fast or vicious foe might very well do something between every PC action. A slower, less dangerous foe might take actions more slowly, letting several PCs "go" before it takes action.
That said, making a move on a PC miss is
always an option - just be aware that it might be the monster doing something (lashing out with a damaging attack, etc) or it could simply be the Keeper complicating the situation (you realize your gun is hopelessly jammed and won't be of any more use to you in this fight).
One thing that will help here is simply experience; you'll start to get a feel for how lethal your PCs are and know how often to have the monster act in order to convey the relative "difficulty" of a particular encounter. If your PCs are mowing through the opposition without breaking a sweat, kick up the frequency with which you take actions on behalf of the monsters.
Finally, monsters aren't stupid. Even if they're not intelligent, they probably exhibit some kind of low, animal cunning. Nobody is going to stand there like a dope while everyone attacks them. As such, you should always be looking for good ways the monsters can limit how many people are attacking them at once. Launching a vicious ambush and then fading away before more than one or two PCs have a chance to respond is totally cool and super unnerving. Likewise, using the terrain to limit the PCs is fun (narrow sewer tunnels being a perpetual fave).
3. There are some situations in which a PC might take multiple actions in quick succession (for instance,
doing something under pressure to slip, dodge, duck, and weave in past the mass of flailing tentacles before whipping out your enchanted sword and
kicking some ass against the monster's actual body). But generally speaking, if it's reasonable to assume that a particular action is going to take some time to accomplish, then it's cool to give other PCs (or even the monster!) an opportunity to do stuff in between the "multiple steps" of another PC's actions.
But for the most part, I like to do things more or less one at a time because I feel like it makes for better narrative flow and leaves "mini-cliffhangers" in the fight (you're past the tentacles and ready to go to town with your enchanted sword; salivating to finally kick some ass, the anticipation as Davis tries to free the virgin from the sacrificial altar before the cultists finish the ritual is killing you!).
4. Everything depends on the monster. If it's slow or weak, then sure, it might get easily overwhelmed; other PCs might simply get to inflict harm on it, no roll necessary. But if that monster is fast or tricksy or has multiple methods of lashing out at the PCs, then everyone is at risk and everyone had better be putting their dice on the line.
5. In general, I gauge it the same way as other harm; is it like getting shot by a handgun? then 2 harm is appropriate. A shotgun or assault rifle? Maybe 3 is appropriate. Being in the blast of a grenade or getting hit by a moving vehicle? 4 harm is not out of the question. Having a roof collapse on you is pretty fucking bad, so I'd probably go 3 or 4 harm. I don't know if MotW has guidelines for falling damage, but those are usually a pretty good gauge for unconventional harm too.
6. As mentioned in the other thread, everything depends on the move's trigger. Look at the trigger condition for
kick some ass - if what the player is doing sounds like the trigger, make the roll. If not, don't. Yes, the player may
want to get the 10+ result, but if they don't trigger the move then no dice ("Yeah, you hit it with your rifle, but damn, the hide on that thing is
tough. You're not even sure you drew blood. You're going to have to try something else to kill this thing.")
Also, for what it's worth, a one-sided application of harm (i.e. shooting at someone who can't shoot back) in AW is NOT the equivalent of
kicking some ass, but rather
going aggro, a completely separate move with a different trigger and different effects. MotW may make a similar distinction.
7. See above. I'd be surprised if MotW didn't have an analog for
go aggro.