Yes in season the CT becomes kind of a zoo -but that is only in high season - late-June thru mid-Sep or so - and trains and boats connect all the villages if trails are closed - you need not hike to enjoy the CT but I'm not sure when you are going - if mid-summer every seaside resort will be mobbed but they have bigger space than these tiny towns hemmed in by sea and mountains.

<Rome, Florence, Cinque Terre, Venice & Paris. Also we want to go to Tuscany one day>

That's still too many places for a 20 day trip.

Florence is in Tuscany so does that suffice for a day in Tuscany?

20 days:

Rome- 4 days
Florence - 2 days
Day Trip to Siena - 1 day
Cinque Terre- 2 days
Venice - 3 days
Paris - 5 days

I think this would be the minimum for 20 days in each place - I took a day out for traveling between bases.

Taking overnight train Venice to Paris could add a day in either. Very possible IMO if a bit quick.

How about:

Rome (4 days) - train (<0.5 days) - Florence (>2.5 days) - train (0.5 days) - Venice (2.5 days) - sleeper train - Vienna (4 days) - plane (0.5 days) - Paris (5.5 days).

ssander

ssander's itinerary sounds sweet!

<Rome, Florence, Cinque Terre, Venice & Paris. Also we want to go to Tuscany one day>

No, that is NOT "too many places for 20 days". You can do it, it's up to you. In fact, I often do itineraries like that, there is nothing impossible about it whatsoever. PalenQ lists such an itinerary and that includes 5 days in Paris, which is quite a lot for the average tourist (I have never spent more than 5 days in a city where I have never been before, in fact). I like traveling around and seeing various places and if I love a place, I come back, but I don't want to overdo it before I've been in a place. You could do another day somewhere if you wanted and not have 5 days in Paris, in fact.

That is much better than some of the original ideas which were too far apart to work well.

This is personal preference, I didn't like Vienna that much myself and 3 days were plenty for me, for example. ssander's itinerary isn't bad, either, except I would never do a sleeper train. I'd much prefer the Italy then Paris itinerary. You can fly a cheap airline on that route like Easyjet (Venice to Paris), it's only about a 1:45 hr flight.