Little round vents are not going to provide much ventilation. For instance even a 4" diameter hole (about the biggest holesaw bit you're going to find) is still only about 12 square inches, i.e. TWELVE 4"-diameter holes is still less than 1 sq ft of opening.
A window is not necessary but it is an awfully good idea; first, because otherwise you will find them quitting laying much earlier in the fall (and resuming later in the winter) than is necessary, and second because it is a good way of providing additional ventilation in summertime with some light for when they are inside.
If you have a windowless coop with no window-sized ventilation openings, it will get powerfully overheated during a TN summer, unless the coop is built in a cave...
Pat