Take the descriptions of the bottles,
So, to follow that new instruction:
A list of all of the other messages in the puzzle, useful or not:
Following the first instruction from the bottles:
Following the second instruction from the bottles:
The beverage descriptions:
The six hint are highlighted in this image:
Fourth hint - solved by @Jens
Fifth hint: - solved by @Jens
The final solution and the logic grid is the following:
Is it here? (in the blue box)
The picture below is used to explain my reasoning:
From the letter:
The best you can do in the swamps of sorrows is that you place the eastern
trading post to
your north . . .
This quote suggests
It can then be seen that
In a similar manner,
Oh, and for the third hint:
I've solved the fifth hint, but it's a bit long for a comment:
One viable solution to the logic grid occurs if we guess that
The last comment above is wrong. There is only one solution. I leave it to you, @Annosz. :)
First off, this is a great puzzle. I really liked spending time on it.
I think it's best to start this problem by finding all possibilities. I also abbreviated each business name.
Next up is all conditionals.
Give me a bit to continue this. I want to make sure everything I've written is correct.
Each node has 4 edges, so is visited twice. We start and end on node A, but it must be visited some time in between as well.
Let's split this up into cases depending on how many other nodes are visited before we come back to A the first time.
This gives a total of:
More explicitly, the routes are:
@Conifers has correctly determined the missing tile with some rules a bit different from my intended ones but still got it uniquely determined so I'm giving him a checkmark. This is the intended answer, :D
Observe that, for each tile:
The properties are:
For the first tile:
And we can have the following as the answer for it (above spoiler):