I think it's a bit busy.
You can manage, but you might get sick of all the noise and crowds of people in major centres.
Your itinerary is full of must-see cities, though, so you may as well check them all out. I didn't care for Venice, but then, I didn't go with my wife. Nor did I have a wife when I went. Nor do I now.
But something I might consider is spending a night or two off the beaten track, in a small town somewhere in between your metropolis adventures, at a little bed and breakfast overlooking a potato field, vineyard, or mountain range.
Get some fresh country air, genuine European hospitality, and a feel for what life might be like on the quieter side of the continent. (I don't think it matters which country you do this in - all the ones you're visiting have charming countryside and I'm sure the people are the same).
I've fallen in love with some of the more remote areas over here (France) and I can't seem to last more than a couple of days in a big city nowadays. Too much BS.
Get out to the smaller towns. People are interested/ing. Things are cheaper.
I'm in a village outside Valenciennes in the north region, an hour from Lille. The people I'm staying with run a bed and breakfast. It's awesome. And for a couple making a stop between major city excursions, I could see it being an enriching thing to do. A nice wind-down, a place to pause mid-way and relax a little.
Or not - whatever tickles your fancy.
__________________
|