Looks great! I haven’t been so I’m just a novice at trip planning, but from the advice I’ve received here I’d be choosing to stay at Nice instead of Monaco…seems “nicer” than Monaco and you can easily make a day trip there anyway…also to Cannes and St. Tropez a little further, if you can put up with the traffic
I don’t know much but that itinerary seems to work and cover it very nicely

So are you flying/ferrying between Bordeaux>Madrid, Sevilla>Morocco, Rome>Athens, Athens>Salzburg, and London>Dublin?
I’d probably drop Athens and save Greece for when I have more time.
I would love to see Krakow, but even if there is an overnight train, I don’t know that I would want to schlep up there from Vienna and just spend 1 or 2 days.

Nice block of time.  Looks okay but a bit frenetic in spots and heavy on the mega-cities.

If you’re starting in Paris, why not fly into Paris??

Why travel all the way to Athens for a couple of days?? Either spend some more time there ore elsewhere in Greece, or don’t bother.

You only need a day or so for Salzburg. 

Zurich is dull – I’d drop it and visit the Bernese Oberland (Big Alps!! – Lauterbrunnen, Interlaken area) instead.

Good that you sandwiched in the Cinque Terre for a little relaxation.

Venice is great but 4 days would be a bit much, I think.

Milan:  Not sure why Milan.  It’s maybe interesting for high-end shopping, but otherwise???  You already have a lot of time in Italy.

I’d add a day to Rome – lots to see – and plan on 3 for Florence for the same reason.

Zagging from Prague to Heidelberg to Munich isn’t terribly efficient – Heidelberg just  isn’t all that worthwhile.  Better to hit northern Bavaria instead – Rothenburg or Nuremberg would be better choices.