Ok, here's my take:
1) As per the OGL you cannot reference Free League settings unless given express permission (as was the case with the YZE Bestiary).
2) You can use whatever labels you want as long as it isn't specific product identity, so just ensure you are using generic terms, such as Dexterity for Agility etc.
3) You can use talents and skills or equipment, as long as they are not 100% setting specific or product identity. Just don not use the wording used in the Free League book.
You do not have to get permission from Free League as the OGL gives you permission to make Year Zero Engine games, as long as you stick to the terms of the OGL. The YZE bestiary was slightly different as it originally started as a third party product for Forbidden Lands but due to some mutual issues it was better to publish as a YZE supplement but the Forbidden Lands terms are used with permission from Free League.
YZE Bestiary - https://www.drivethrurpg.com/product/320924/The-Servants-of-Memory
Forbidden Lands Blog - https://is-it-a-monster.blogspot.com/
Session Generator - https://perchance.org/fl-session-generator