I’m not sure I need to say this, but still: SPOILER WARNING
I’m pretty sure you can interact with the tapir god/old man as early as day one, if you go straight for the salt plains (could be wrong there, though). Additionally, you can get the pelt and the cross in the same trip to the flooded town if you have the remains and you’ve visited the tapir god before.
Anyway. From my runs of the Hinterlands, I found three big areas where your choices seem to have an impact at the moment, and as best as I can tell you can only ever get 2/3 of them 100% accomplished in any given run (if anyone has a way to do all three, let me know!):
- Return the tapir god’s pelt
- Put the 12 to rest with the remains
- Develop Pedro/Oscar’s relationship
The first two are pretty straightforward— you start the event at the first location, get the required object(s) from the flooded town, and then head to your last location. For the third, picking events that make Oscar and Pedro bond causes their relationship to change pretty clearly (going to the tailor, visiting Storm’s house, and heading to the church (maybe?) seemed to do it for me).
I’m sure I’m missing some secrets, but there are achievements for completing each of the two plot threads, and a lore note that gets added to your inventory if you go to the library and read non-fiction.
Apparently, plot threads like the missing kid are possibly coming in some point during a later patch/future chapter, and your choices in the Hinterlands will set up some of those things! We’re all in the same boat regarding how those’ll work, though, so I can’t offer any help with that. Regardless, I hope this is at least somewhat useful!