The rules don't appear to specify whether monsters are drawn one-by-one or all at once when you have to draw multiple monsters. Is anyone able to point me to a clarification of this rule?

Also, the rules in the core game only state you need to nominate which gates monsters will spawn at in advance if you're going over the monster limit. Does this mean you're free to draw and then choose gate placement afterwards in all other circumstances (allowing for source gate may not have less placed than other gates rule)?

Quitch,

I'm unaware of any rules, though the FAQ may make a point of answering this one. Otherwise, draw and place...you should never draw, check it out and then place on a gate.

Cheers,

Joe

Rules are foggy in wording, but I'd suggest not abusing of foggy rules to our own advantage. You pick the monsters one-by-one, and you decide where to spawn what before looking at the token

I concur with the others. The game defines a "Monster Cup" (which can be any opaque container sufficient to hold all the monsters in play.)
The clear intention here is that you cannot see the monsters in the cup until you draw one out.

The rules also define the process for drawing a monster out of the cup. They don't define the process of drawing multiple monsters at once, only for drawing a single monster.

The fact that circumstances in the game can lead to multiple monster draws being called for based on a single triggering event therefore suggests to me that you are performing the act of drawing one monster multiple times. Each draw needs to be resolved in full before starting the next, and that would include declaring which position you're drawing for.

FFG has a well-known habit of adding extra rules intended to "clarify" specific cases, when the same rule in fact applies to all cases, and this ends up causing confusion in the long run. I'm inclined to think this is one of those. To wit: they specifically say you need to nominate gates first when you know you're going to exceed the monster limit, but I expect that if you contact FFG and press them on this, they will likely say that you need to do this anyway, even if you're not exceeding the monster limit.

Finally, there's the popular fan rule of "Arkham's Razor": when in doubt about the rules, always choose the option that least favours the players. Since this is a co-op game, this policy will keep the game harder - and therefore more interesting - for as long as possible. Once you can beat a co-op game with ease, you tend to stop playing since there's no challenge.