MC,
I suggest you research the time it will take to go from one place to another. Be sure to include not just flight/train/drive time, but check-out time, going to train station or airport, and time to get to your next lodging, and check-in time on arrival in new location. Please don't underestimate the size of Europe and distances between places. (For example, the country of France is about the size of California.) I also suggest you choose just two countries, especially if you choose Italy with your six locations there. That alone would take about three weeks. You need time in each place to actually enjoy it and not just check a box.
All that aside, my husband and I had to postpone our honeymoon for three years, but were able to spend four months in Europe in 1974. We bought a VW so we drove everywhere for three months before shipping our car home (that took a month). We had the time to visit eight countries, some for three days, others for a month. But if we had just a month, we would definitely stick to just one or two countries so as to get the most out of our visits there. And we would not have been able to see all there is to see in each country. We would probably pick just four cities or areas to see. Thus, I would not try to add countries, I would subtract some. It is already very strenuous.
Congratulations on your upcoming nuptials! Have a wonderful honeymoon in Europe, and I hope it will only be the first of many trips there!
Bonne chance!