Creating a BP Actor That Creates AI Navigation

Hello,

I allow the player to create BP actors that are “paths” (road, trail, etc.) that I would like to allow the ai to walk on. I want the ai to only be able to walk on the path actors.

Questions:

Do I need an initial nav mesh bounds volume that covers my level?
If so, can that be set to “null”, then my path actor has a modifier set to “default”?

Can a nav modifier in the BP actor be used to create the navigation bounds on its own? (without initial nav mesh bounds)

Basically how can i create dynamic objects that can expand where my ai can walk?