attic vent questions

I have an approx 1500sf hip roof on a single story ranch and I'm about to install an electric attic vent in place of the middle of 3 current passive vents which are only about 50si each and have a few questions.

First, what is the best way to block off the other 2 passive vents so the fan does not suck air from them? I'm not reroofing soon so external appearance will probably remain the same. I do have a partial bundle of shingles though if its not too hard to patch. (I'm adding plenty off soffit vents so I'll have adequate intake)

Second, what kind of roofing nail should I use? There seems to be so many types and I'm not sure which to get?

Thanks!