We are not travel arrangers here but will give you some thoughts. Get a map and put some pins to give you some idea of geography. For example Florence would be a better choice than Venice because it is more in-line with Paris. Less traveling. Second consider rail travel over fights as being more time efficient. Our benchmark is five to six hours. If a train ride is more then I will look at flights. Some travelers will have a slightly lower trigger point but that works for us.
Don't know what you mean that some cities don't have a lot of sightseeing. That needs a better explanation as each of the cities has enormous sightseeing opportunities. Over the years we have spent a month in Rome and still have a lot to see.
You could do Rome, Florence, Milan, Zurich, through Switzerland, and on to Paris. Fairly straight line with easy travel via train. Obviously, swing a little further south and hit C Terra (instead of Milan) Genoa, Nice, and more of southern France and then on to Paris. You have a lot of option but the one option you do not have is --- "Seeing it all !!!" So plan on returning. Planning to return makes the decision marking process much easier for the first trip. On our first trip my wife's constant refrain was, "We will see that next time." It made it easy to pass things by.
