Statistically, you're only hitting kobolds 2/3 of the time, give or take (AC 12).
Not sure where you're getting that figure from. Short of making a completely inept character, each PC should have a +5 to hit.
And they have 5 hp. Unless every one of your PCs has a +4 ability modifier (and even then), I don't see how you're taking out 4 or 6 kobolds in the very first round.
With five players, some of whom (like the monk) have multiple attacks, it's pretty much a given. You don't need a +4 ability modifier. Most PC's will be getting a +3 damage bonus to most of their attacks. Even a d4 has an average of 2.5, making the minimum average damage 5.5.
Hell, for us it sure did. With advantage, and a +4 base to hit, they were hitting us nearly every time. Did all of your PCs have AC 18 or something?
Nope, but the ones who did tended to be the ones who rushed into melee whilst the others stayed at range.
How do you figure. Your extra monk attack doesn't get ability modifier damage to it unless you also have the two-weapon feat. My interpretation is that it's treated like any other bonus off hand attack. So how does 1d4 dmg take out a 5 hp kobold, assuming you're hitting with every attack anyway?
Sorry, but you'd be wrong about this. This has been clarified and even before then, the consensus was very strongly in favour of the monk getting their ability bonus damage.
Yeah, or wiz tried burning hands too. Took out two kobolds that were in range, but because of that ended up in the front line (since you have to get close) and got skewered by the other remaining ones. A AC12, 6HP PC didn't last long against kobolds that attacked at advantage.
In a number of the encounters it says how the creatures are organised, like at the front or back door of the temple, or at the Sally Port gate. There are multiple opportunities for bunched AoE.
Also, that's great for one encounter, but what about all the others? You can only do those things once.
Short rests are allowed. HD healing, healing pots (bought at level 1 with starting gold... always a smart idea), and powers renewed. The warlock, for instance, is a powerhouse after every short rest.
Eh, I've run/played in it four times so far. It's a small sample size. Perhaps the fifth, sixth, seventh and eighth times will be a disaster. I doubt it, but we'll see.