So yeah, I would say just go ahead and read everything for that chapter just in case something is not in the order you would see the things. Example, the Dallis hammer achievement was in Part 2 of the Fort Joy and someone ended up missing the achievement (it's fixed now, it's in part 1).
I would highly recommend that you read all of the chapters achievements in the missable section if you want to go for all the achievements there. So the in the achievements you can miss parts, they are not in any particular order. When you create your character, that character is now your main. Example: you recruit Beast into the party, he is then a side character. I say this a lot in the guide and all it means is that a side character is a character you recruit into your party and you now control. Most are hidden unless you get the achievement, so I felt that I needed to share what is actually there. That just means the Description that is given with that achievement. Under each achievement you will see a 'Desc:'. The ones in that section just have to do with the ones you can miss. Example: In the Nameless Isle section there are more than 5 achievements there. All the ones in the other sections, are achievements that you could potentially miss. The achievements in the story section, are ones you will get when just playing through the main campaign.
In this guide the achievements are split up into sections. Quick Guidelines to my guide just incase I come off as being a little unclear.