Jon,
Your revised Itinerary looks good. However, I still wonder whether open-jaw would have been a better idea, considering you'll have to use both time and money to return to Paris.
If I'm reading things correctly, this is what you're planning:
Day 1: Flight to Paris
Day 2-4: Arrive Paris; touring (were you planning to buy a Paris Museum Pass?)
Day 5-7: Train to Gimmelwald (via Interlaken Ost) - one train to consider departs Paris Est at 08:24, arriving Interlaken Ost at 13:57, one change in Basel, reservations compulsory. Do you know how to get from Interlaken to Gimmelwald?
Day 8-9: Train to Lago di Como (Varenna?) & touring - one train to consider departs Interlaken Ost at 08:01, arriving Milano Centrale 11:35, two changes in Spiez & Brig, reservations compulsory. As I wasn't sure if you'd be staying in Varenna, I only searched to Milan.
Day 10-12: Train to Cinque Terre & touring - one train to consider departs Varenna-Esino at 08:37, arriving Monterosso at 14:54, three changes in Milan and Genova. As I wasn't sure which village you were staying in, I chose the closest one in the north (which is the direction you'll be coming from).
Day 13-15: Train to Venice & touring - one train to consider departs La Spezia Centrale at 07:52, arriving Venezia Santa Lucia at 12:33, one change in Bologna, reservations compulsory. Travel from whichever village you're staying to La Spezia is easy, and the trains run frequently.
Note: the train times shown are of course subject to change. Don't forget to validate your tickets!
I'm assuming you have a Hotel booked for your last night in Paris (don't forget to tell them that you'll be arriving late).
Cheers!