As far as attic ventilation vents go, gable end vents by themselves generally don't do what the homeowner expects. Air exchange through such vents is minimal. The best arrangement is with a ridge vent and either continuous soffit ventilation or at least vents in each soffit bay. With both ridge and soffit vents, it is generally advised to close off any gable end vents, as they interfere with draw of air in the soffit vents.
On the subject of powered attic ventilation fans, this is a good read:
https://www.greenbuildingadvisor.com...tic-ventilator. In general, it isn't a good idea, and it's the wrong way to address a problem.