Is there some sort of guide or hints around to get all achievements (particularly Memories of Nyx and Kanathar)?
Yep, right here: https://dawnofcorruption.wiki/index.php/Main_Page
oh, well then this might help you instead: https://dawnofcorruption.wiki/index.php/Endings
For the imp you need to be submissive to the imp fyi