I think you'll find two distinct camps on the closed/open cell debate. I suspect you will be happy with either decision.
Do not ventilate the roof. Uncontrolled ventilation is to be avoided whenever possible, and since you are going with spray foam you can.A blower door test should also be performed before drywall to assist in finding leaks missed by the foam installers.
Design an Energy Recovery Ventilation system into your home. Ideally you'll continuously pull stale air out of your bathrooms and deliver fresh to bedrooms.
- This is very very very important.
- You need to design controlled ventilation for health, safety, comfort, efficiency and durability of this nice home.
For more information:
Read "I'm converting my attic into a non-vented conditioned space. Should I use open cell or closed cell foam to insulate?" a Q&A answered by Steve Saunders.