Look at SuperSuns from Sunlight Systems- ...
I'll look at the SuperSuns (as I can find 'em), not the SuperSun II.. tho I'm having a problem Googling 'em. And I'll look at some bathroom exhaust blowers.

Guesstimate that 70cfm throughput is gonna be overkill, depending on exterior temperature.
This will be a basement grow where temps are maybe 65-70F that time of year. So, I figure there is a giant heat-sink in the basement to dump any excess heat. I think I appreciate when folks say, "Basements rock!". With minimal basement exhausting, and perhaps some kind of CO2 enrichment (or more accurately, some CO2 remediation) I'll be fine. I wish I could measure/monitor the CO2 cheaply.

Ya might wanna flow it so that heated air moves from flower to veg- if it runs a little warmer in veg, it's not the end of the world.
I can appreciate that the temperature in the bloom closet is much more important/critical than that in the veg room.

I'll try to post about my plans, otherwise I'll post some kind of log here. I've really learned a lot here so I feel that most of my plans will get a few nods (if not a few nod-offs!).