The most recommended vents for this particular style are open soffits, like this: https://www.backyardchickens.com/threads/coop-modification-recommendations.1517556/#post-25543595I can easily make modifications for additional ventilation as needed. Have the coop primarily for laying eggs and protection against predators.
I'd also consider larger, top hinged vents sort of like these (this person put in a lot!), so the top hinged panels help buffer wind and rain, but can be opened fully on hot days, or partially closed when weather isn't great: https://www.backyardchickens.com/threads/coop-ventilation.1452812/page-2#post-24868607
If you need to add a fan, make sure it's one rated for use in a barn type setting. You should not need to provide heat in your climate, unless you're brooding chicks. Healthy adult chickens do fine down to 0F as long as they have a draft free and dry place to sleep.