The total attic venting of 1/300 is if you have a vapor barrier on the ceiling. If no v.b. present use 1/100. You are figuring the ridge vent numbers wrong. A good, high end ridge vent with baffles gives 18 sq.in. per ft. x 36' = 648/144 = 4.5sq.ft. So with 1/2 intake at soffit, and 1/2 exhaust at ridge, you are just right. As said block the gables.
Ice dams are forming because you are losing heat from the ceiling or just from the fan. I would route it out the roof above rather than to the soffit where it is recirculated into the attic by the intake vents. Did you seal all pipes and wires at the plate line walls?
The styro baffles have 25% less air flow than the plastic from the other box store. And the plastic ones protect the ends of the insulation pile from the cold soffit air there: Berger Building Products
And you won't pay extra for the special wall separator: Windblock
Energy Savers: Attic Access Insulation and Air Sealing
Be safe, Gary