What a great looking space! Your greenhouse and mine have a lot in common: Lean-to style facing south in zone 6 in the same latitude. Mine is about 6.5 ft wide and 22 ft long.
I thought I would need to add lights for winter but its full sun even on the shortest days. And if the sun is shining, the greenhouse is heating. In winter, you may have to add a utility heater for the night time though.
Yes, open those vents and the door that leads outside and leave them open until fall. Put fans in. I use clip fans attached to the shelves. Its important to keep the air constantly moving or you will have mildew problems. Drainage is an issue - maybe put saucers under all your plants and water carefully? Is the floor sloped? Daughter has no drainage either and the bottom of her walls are wood siding with some sort of coating on them to make them waterproof. She has saucers under everything and tries to keep the floor dry. Luckily, a little water spilled on a concrete floor won't cause damage, its the constant water against the wall that's an issue. Even though my greenhouse has drainage, I solved the problem of damp walls by tiling the wall up about a foot - like a backsplash in the kitchen.
I don't like wooden benches or shelves because they harbor bacteria, bug and diseases in the grains of the wood. I use metal shelves but my greenhouse is built in such a way I can hook them directly to the walls. You could use metal bakers shelves - that's what my daughter uses in her greenhouse (mine are metal closet shelves).
