How do you insulate an attic in Victorian House in Massachusetts?

I could use some advice on how to add insulation to my house.

My house qualifies for a state of Massachusetts program to add cellulose insulation to my attic, but I would need to add vents in the roof in order to meet the building codes.  But adding vents would entail cutting at least 4 holes in the roof, and it is not clear that would provide adequate ventilation.  Another option is to add closed cell spray foam insulation to the underside of the roof and not install vents.  But spray foam has its risks and drawbacks too.

The house is a 3 story, 6000 square foot Second Empire Victorian built in 1882.  It has a mansard roof with shingles, and the top roof has a 4/12 pitch, and is covered with a Firestone 60 mil TPO fully adhered roof which was put on top of 1″ polyisocyanurate insulation over modified bitumen roof.  When we installed this TPO roof in 2005 I eliminated 3 original vents which probably was a mistake.  There are no vents or soffits. 

My roofer originally recommended two Lomanco Whirlybirds be installed.  But a Lomanco engineer recommended against his own vent because there are no soffits to provide intake. He suggested I get gravity vents.

I’m considering adding 4 Gravity Vents: two installed at the highest points of the roof, two at the lowest points of the roof.  But the difference in relative height between the highest and lowest vents is not that much. 

I have consulted with some building scientists at the University of Massachusetts.  I received conflicting advice.  One said adding the vents would be ok.  But another recommended against adding 4 vents and suggested I use closed cell spray foam to the underside of the roof.

But I have seen a number of reports of class action lawsuits against spray foam industry.  If the spray foam insulation is not applied exactly right, it can off gas toxic gases, according to reports.  I don’t want to take a chance destroying my house with this kind of spray foam.

So what to do?  Are there spray foams that don’t emit toxic gases even if the foam is applied incorrectly?  Do you think spray foam is risky?