1

have you ever been to Venice before?? if the answer is no, then imho you should spend at least 3 nights there. You could decide to cut one of your days in Slovenia or in southern France, but it also depends on what your interests are. I just tell you that this promises to be a beautiful journey, and Venice could easily be the highlight of the trip. And if you can, try staying in Bled, its surroundings are really beautiful and I guess it's wothy to spend a night on route from Venice to Ljubljana. And then, add Plitvice National Park in Croatia, possibly cutting out a night in Split. Might be a bit tricky to get to by public transport, but definitely doable, and it's a really beautiful park, google it for some pictures!

By the way, I see that you'll just bypass northern Italy, I know you have a schedule, but you might consider taking a stop-over or 2, there are beautiful places en-route from Nice to Venice, ie Parma, very nice city with good art and great food

2

What do you want to do at Geneva during 2 long days? A day trip to Interlaken would certainly not be a good idea, as there is absolutely nothing to see, except some mountains, more or less similar to those you will see at Chamonix and along the TMB trail.
As to PACA, you don't tell us how you will go there from Chamonix and what you will do there: no comment possible.
Why do you want to go up to Dubrovnik, if you have only 4 days to spend for the whole trip from Ljubljana up to there?
It's ridiculous to go to Venice during super high season for a pizza and a gelato only!