#1 How do I understand and define my own zone 2 limit? As well as what are the potential benefits of zone 2. Click to view discussion.
#2 Here is a long discussion on finding your limit as well as important pre-ride fueling. It goes into different deep ideas of zone 2 with a guy that is an expert. View Discussion
#3 Maffetone Running vs Cycling and Heart rate changes (HRR)
#4 Another discussion on setting target HR
EDIT - adding below
#5 - very long discussion with a lot tangents but might be useful How to test AeT efficiency