Given the Maine climate, you will want to try and maximize your R-value.
- Guessing that the roof rafters are only 2x8 based on the 1914 construction date, I would highly recommend using about 5-6" of closed cell spray foam.
- If you have 2x10 then you can just use 10" of open cell spray foam.
Venting is not necessary, but if the rest of the house is airtight you will want to install some sort of air exchanger to bring fresh air into the house.
But you will not need to vent your roof any longer as long as the foam is installed properly from the top of the sill plate to the ridge.
For more information:
Read "Should we insulate the attic of our 1926 bungalow with spray foam insulation?" a Q&A answered by Anthony Addesso.
Also, 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.