In general, the more the venting, the better. In the ideal case, the
attic will never be above freezing unless the outside temp is too. In
other words, the attic should be same temp as outside in the best case.

The only caveat is that sometimes it is better to strategically add
vents to get good cross-ventilation, rather than just haphazardly. The
recommended way is a continuous ridge vent (across the whole roof), and
continuous soffit vents (a single opening along the entire soffit).
What you have done is most of the way there...