Hello all, I am looking for some feedback/advice on a new roof and existing attic design, specifically what if any changes need to be made.  Apologies for the long post.

House is 90 years old located in climate zone 4A, 1.5 story
Existing roof is high pitch (10:12) asphalt shingle, tar paper, and T&G sheathing
Existing roof eves (soffit area) are located at the ceiling of the ground story and are finished (no venting)
Existing roof has a ridge vent
Existing roof has partial dormers on each side (no venting in these soffits)

Attic is accessible via open stairwell (nothing blocks air movement)
Attic is partially conditioned with a knee wall separating spaces
Cross section of the conditioned space from inside to out is 3/8″ board, foil faced R-21 fiberglass, baffles between some of the rafters connecting the unconditioned space to the ridge vent, then T&G sheathing, tar paper, and shingles

The attic floor has also has paper faced R-21 fiberglass 

The underside of the T&G sheathing and rafters show no signs of moisture (meter testing of wood has it around 4% +/- in winter) but where the dormers meet it appears water has infiltrated in the past (staining)

Also A/C for the upper floor is installed on one side of the unconditioned space with heavily insulated ducts, intake is located on the ceiling of 1st story 

We are planning the following near term:
New asphalt shingles with synthetic underlayment, specifically TigerPaw for breathability, flashing, ice dam etc.
Installation of mid roof intake vents on both roof pitches located above the unconditioned space

We are planning the following longer term:
Installing additional baffles in the attic between the rafters from unconditioned space and the ridge vent
Installing higher r value insulation in the accessible parts of the attic floor

My concerns are that there are no issues now and installing intake vents will exacerbate any stack effect in the house and that with the open stairwell between the 1st story and attic, heating and cooling will be greater.

Thoughts?