3). Paris, France
4). Brussels, Belgium
5). Lucerne, Switzerland
6). Munich, Germany
7). Prague, Czech Republic
8). Salzburg, Austria
9). Ljubljana, Slovenia
10). Venice, Italy
11). Florence, Italy
12). Rome, Italy
Number 3 to 4, normally by Thalys or occasionally TGV. Thalys reservation price alone is very near the price that can be found for a normal ticket - plus you pay for pass day.
Number 4 to 5 - Usually the first bit of that journey - if you don't fly which may be faster - by train will Thalys as far as Koeln. See above for Thalys restrictions.
Number 5, are you going all the way to Switzerland and not going to the Alps? Eurail passes don't go all the way.
Numbers 10, 11, 12 - local trains in Italy are extremely cheap. Fast trains require a โฌ10 per leg passholder reservation; the tickets can be be as cheap as โฌ9 to โฌ19 per trip and include the reservation.
None of the watertaxis, vaporettos, or gondolas are covered in number 10.