Seeing your soffit vented - Yes, I would cut those boards out where the perforated soffits are and install those cardboard/plastic vent shoots to the roof down to the soffit. Then plug up by installing the board back in on the edge of the wall plate and cut out around the soffit vent shoot (Or used spray foam cans to seal up the area - easier / quicker yet). You then should add more venting at the roof peak line . . . . 
As far as amount of insulation - You can never have enough in an attic, even in your climate, it'll keep the heat out of the house.