Q.Peonies
When the flowering is done, should I cut them off and plant the seeds?

Fall is the best time to cut down your Peony plants, they can be cut down to about 3 inches above the soil.
Peonies will shed their leaves when the weather cools.
Propagating Peonies is done from division.
Here are some links with more information.
https://www.gardeningknowhow.com/ornamental/flowers/peony/peony-care.htm
https://www.gardeningknowhow.com/ornamental/flowers/peony/dividing-peony-plants.htm