Should the foundation wall be insulated when encapsulating a crawl space, or not?
I think the accepted best practice is now to make crawl spaces part of your conditioned living area.  Insulate and allow air to circulate like you do in the rest of the house.  The best practice for new builds may not work depending on your construction details.  You should check out how Risinger Homes out of Austin Texas handles it.
https://www.youtube.com/watch?v=5n4K170f56I