It's really hard to say just what you will need to do for ventilation, observation is best. I keep a thermometer in coop. Go out into coop during severe weather(rain, wind, and snow) and see how the air is moving around in there and if there's any rain infiltration, you should be able to see any...
I wouldn't bother insulating, drafts should be observed and managed.
I use cardboard baffles in winter, on mesh 'ceiling' of coop, right over main roost which is close to open eave.
You must mean the ventilation article in my signature?
Some good info there but all not carved in stone.
Here's a...
Fallacy...adequate ventilation makes 'holding heat' moot.
Roosts in run are fine, keep them lower than the ones in coop,
they prefer to sleep on the hghest place.