You can add you location to your profile, and then it's always there. Location and climate matter, and what works for me in Michigan might not for you in California.I’m located in super northern, coastal California (Arcata, CA).
Just as important is predator proofing. Figure to cover openings with hardware cloth.This may be a dumb question, but how do you weatherproof the ventilation? Just by making sure you have a long enough overhang from your roof?
Keeping weather out... Overhangs and awnings work well. You don't want rain or snow (if you get snow) to blow into the coop.
Before you put this in its final location (if it's moveable), note which direction brings most of your weather. Most of my wind and rain come from the west, so I have bigger openings to the north and south.
I second this advice! Bonus: you'll get to have chicks (the really cute stage of chickens) twice. But then you will have to integrate them into the existing flock.8 should be doable in there but I'd do 4 and then another 4 a year or two later to help with more consistent egg production over time (assuming eggs are a priority for you).