Insulation right up against the roof underside is a no-no in most designs, certainly with a venitlated roof. However, to quote Popeye from your house's standpoint, I y'am what I y'am, so you work with what you have got. A Don said - go with ridge vent.
Ridge vent is far better for ventilation, cheaper than a bunch more round roof vents, and eliminates the leak potential from additional vent penetrations - so go with the ridge vent. Especially because it is cool and unused mcuh of the winter, be sure to get one with baffling to prevent snow blowing in if your winters have snow. Unless this is sprayed foam insulation, due to insulation settlement (especially if it gets wet) there will be at least a minimal airgap under the sheating to provide airflow space to help dry out any moisture that gets into your sheathing or insulation.
The only reason I could see needing more round roof vents is if there is blocking or someroof structure that blocks airflow to the ridge, then those specific locations might need roof ventsif the air cannot otherwise rise and escape.