In terms of balancing, I'd say the toughest thing was getting the right balance in the number of locations that players can explore.
We needed to have around 12 locations at least so that players wouldn't often stumble on the second questline by accident, but if we went too far the Hinterlands' content could become too spread out and things wouldn't connect. We also wanted to avoid going too far because we'd start using our not-so-great ideas just to fill stuff.
Overall the Hinterlands' writing had a lot of thought put into cutting out "filler" content — or what constitutes filler for what's an intentionally meandering narrative. A few times I scrapped content because it didn't have enough going on even if it was a serviceable scene.
Balancing how much to reveal or not was also tricky. Believe it or not, before release I thought things were too obvious! I'm glad we didn't change things, though, seeing the discussion going on I feel that we hit the sweet spot.