I would open the soffits.I'm thinking of running it hot roof and sealing it up and then setting the vents exactly as you say but closed soffits
The ventilation isn't for the roof shingles.
It's for the birds to prevent frostbite in the winter and keep them as cool as possible in the summer.
My coop has all the spaces between the rafters open paired with 2 permanently open gable vents and a ridge vent with two windows away from the roosting area cracked open and the two permanently open pop doors. They need this to stay healthy year round.