If your supply of leaves leaves you wanting for more, use organic mulch instead of leaves.

Paniculatas are more winter hardy than macs. In a pinch, winter protect macs only with leaves.

In a pinch, if you cannot winter protect some of them, put those in the garage.

I have not tried keeping outside cuttings that young so I will let other comments. Your winters should not be that cold though. Long term wether forecasts for winter should be out in Aug-Oct, Watch the newspapers or weather.com

I'm in Jersey (7a/6b) and I've found my cuttings do better in the garage their first winter.

I had some macs and pans rooted in June of 2016. I planted them in pots and transplanted them in the ground just before the ground froze last winter without any protection. All of my cuttings survived this year. In fact, they are now the size of a 2gal plants that you would buy from nurseries. My macs have around 8 blooms on them and my pans are all covered with blooms.

The previous year I lost almost all of my rooted cuttings when I winterized them in the garage.