Ok, I am going to play along. Upfront, I have never done this and couldn’t (so haven’t even researched). And I can’t really see how you could do it all either. But you could do some of it and save the rest for later.
Since you already have tickets into Venice: why not skip Rome and Tuscany this time (wrong direction and half your time)? Next, start with some basic homework about budget flights between locations. Go straight from Venice to your first city. Which one would depend on available flights and I don’t know since I haven’t done this. For example, a 30 second google search shows Venice to Nice on Easy Jet (didn’t check any further for dates and times). You might be able to do something similar to Vienna.
Choose 3 cities/locations for 3 nights each, and include spending a day transitioning = your trip.
It’s all about your top priorities, workable transportation between them, and your budget. Although many people on this forum travel a lot and there is a mass of collective knowledge, regulars wouldn’t try to hit ALL your list for good reasons. And no one here knows how you would order your top (realistic) places to see nor what your budget is.
Hope that helps as you do further research! I do think seeing some new places is a great idea!
(Not to be mean, silschleich): @princess pupule, I actually laughed out loud “miracles can happen but I doubt this vacation will”