ACT 2 SPOILER
I didn’t realize until talking with friends that you could win the abduction fight at the Harper camp in Act 2. If you don’t kill the baddies in time, the safe bubble collapses, and everyone in the Harper camp gets shadow cursed, and you have to fight your way through them. It’s genuinely heartbreaking and horrifying.
I finished the game once, have 2 co-op games running with friends, and just started a modded playthrough where the whole party is Artificers. I highly recommend giving some of the mods a try once you’ve played through vanilla. They’re super easy to install and add so much fun an variety.
I don’t think so - I’ve been playing since early access and you can block doors, it just usually takes 2 people to do so.
Putting Jump on a bonus action basically fills the role of tumbling through enemy (and ally) spaces.
There are two places you can go to trigger Act 2, either by going into the elevator in Grymforge or continuing into the Mountain Pass after meeting/fighting the Githyanki.
There’s a popup in each area to be sure you’ve finished what you want to, as moving to either area progresses the story and quests, and some stuff you don’t do is left undone.
There’s a similar popup between Acts 2 and 3, though there’s only one way to go for that and once you do, you can’t fast travel back to anywhere in Acts 1 or 2.