I'm not sure I understand... maximum ventilation is relative to time of year, right? In summer you need truly maximal ventilation to deal with *heat* as well as humidity. In winter you are only dealing with humidity; and in colder climates you probably want to limit the ventilation to just what's required to keep air quality good, rather than leave all the walls hangin' open to chill the birds and blow them across the coop
Would leaving both window open not be too breezy?
Yes, that's why I don't think a system that relies solely on windows is ideal for places that get cool in the winter. It is real good to have ventilation openings that are high on the walls, preferably tucked up under the eaves of the roof. THOSE can stay partly or totally open during the winter -- their position gives you greater 'bang for your buck' in terms of flushing out humidity, and minimizes draft at chicken level, and if protected by eaves they won't let in rain or snow the way windows can.
What about a one inch gap all around the roof?
That is certainly one of the ways of doing it. Remember though that you will sometimes want to shut off the upwind side(s), so it is good to make sure that a) that's easy to do, and b) it'll still leave you with a good amount of ventilation capacity to play with. An inch around the top of a 4x4 coop is only 1.3 sq ft of total area, although effectively it will be even less because a) there will be obstructions such as studs or rafter tails, and b) air does not move through a very narrow opening as freely as through a wider one.
There are a variety of options, but personally I'd suggest (for your size coop) openings 3-4" high across the tops of most of the four walls, or slightly larger ones on the two downwind walls, with flaps to close them partly or totally when desired. Ideally a roof overhang would protect them from blowing rain/snow; if not, and if there isn't a roofed run to ventilate into, you might end up wanting to rig some sort of hood or at least louvers to reduce stuff blowing in. Be aware that most commercial louvered shed vents give you MUCH LESS actual ventilation area than they seem -- look at the size of the actual openings (how much area can you see sky through?), not the size of the item as a whole.
Good luck, have fun,
Pat