Perhaps for this reason (moisture getting trapped in outer osb layer) Kingspan TEK systems are built with PIR installed internally. The supplier we used has the u-value data for different thicknesses of PIR on this page https://www.clays.com/sips-technical-data
Remember there is no such thing as a daft question, daft is not asking, we all had to start somewhere 👍 yes Coombs and eaves trays best way to stop birds getting in but still allow ventilation, eaves trays support roofing felt that often fails near the gutter so will extend the like of you roof.