A few additional comments.....
As this is your first trip to Europe, I'd highly recommend reading Europe Through The Back Door prior to the trip, as that provides a lot of good information on how to travel in Europe. The country-specific RS guidebooks are also a good idea for planning touring (ie: some sights are closed one day per week), city transportation, etc.
In your last reply, you asked about the cost of doing the trip by train. Did you consider the exorbitant drop charge for renting a car in Venice and dropping in Paris? I didn't comment on the point of using trains earlier as you had stated "don't tell me about the long drive". Especially for shorter duration trips, travel by train is by far a more efficient use of limited holiday time. The high speed trains travel at up to 300 km/h which is much faster than any car, and you'd be able to relax and enjoy the scenery, wander about to stretch your legs or have a nap.
The cost for trains will vary. Especially in Italy if you pre-purchase tickets on the high speed trains well in advance, it's possible to get some great discounts. However, the cheapest tickets are non-refundable and non-changeable once purchased, and are specific to train, date and departure time so you'd have to be willing to commit to a specific train. Tickets for the slower Regionale trains have no discounts, so you can either buy those in advance or just buy on-the-spot.
There are some "caveats" to be aware of when using trains, buses and other public transit in Italy. For example, when using Regionale trains or Vaporettos (Venice), tickets must be validated prior to boarding or you'll risk hefty fines, which will be collected on the spot!
In order to provide more info on trains, it would help to have a more detailed idea of your Itinerary. To provide an example based on what you've posted so far, there's a train departing Venezia Santa Lucia at 08:20, arriving Lauterbrunnen at 14:55 (time 6H:35M, 3 changes at Milano Centrale, Spiez and Interlaken Ost, first segment via high speed FrecciaRossa). While that might sound daunting, it's actually very easy. I couldn't check schedules for the time you'll be travelling as schedules for the latter part of June haven't been posted yet. There are numerous other trains on that route, but the one I mentioned above is one of the shortest and easiest.
For the trip from Switzerland to Paris, the usual method is a regional train to Basel SBB, and then high speed TGV from there. There are numerous direct (no changes) trains each day, with a travel time of 3H:03M. The trains often arrive at Paris Gare de Lyon, so you'd have to take a Taxi or whatever from there to your hotel (a good idea as I wouldn't recommend driving in Paris). Paris has about six large rail stations.
I checked the schedules using the Bahn.de website, which covers trains all over Europe. If you wish to pre-purchase tickets, I normally use the www.trainline.eu website.
Hope this helps.