Hi Tonychacko -
The forum moderators and i frequently recommend the train from Paris. A trip with no change of train from Paris gare-du-Nord takes between 3 hours 3 minutes and 3 hours 40 minutes to Zürich.
If you take into account the time to travel to the airport in France, as well as the need to be at the airport well before flight time, you can see that the train is competitive on time, especially since you can arrive directly in Zürich main station. From there to Interlaken is on hour and 55 minutes .
You can also make one change at Basel and catch a train to Interlaken Ost, taking 5 and a half hours with no other changes. That is faster than going through Zürich.
If you travel from Zürich Airport to Interlaken, there are frequent trains, which go through and have one change at Bern. Some have a change at Zürich main station; some only require a change at Bern. That trip takes 2 hours 10 to 2 hours 20 minutes.
I have gotten all of this information from the timetable:
Check it out. It is incredibly useful. Please read the instructions page. The timetable is full of useful information, but that is sometimes a few layers down in the menus.
You can use the timetable to understand the other journeys, including the journey to Italy.
Whether to stay at Zermatt or Interlaken is a matter of personal preference. Both are nice. Read about the cities and the Jungfrau region in the link I give below in this posting. Zermatt is smaller and more concentrated and is in the Alps. Interlaken tself is nt much of a scenic tourist destination. It is best as a gateway to the Jungfraui region with its scenic villages and wonderful scenery. The Jungfrau region is quite large, with more places to go at various altitudes, and Interlaken has good rail connections to the rest of Switzerland.
Especially in late Winter or Spring, there are often clouds at the Jungfrau. The weather is unpredictable more than 24-48 hours in advance. It can change very quickly. Clouds and fog up top can ruin the views. However, it may be foggy at low levels and clear up above 2000 meters. the hotels and train stations and tourist information offices have up to the minute information.
To improve your chances for good weather, it is usual to plan for a few days in the region, hoping for a clear day.
Train time between Zermatt and Interlaken is about 2 hours and 20 minutes by the new, faster tunnel between Spiez and Visp.
To Italy -
From Zermatt, the route to Italy (Milano Centrale) is convenient. Go to Brig and catch a train the Simplon. From Interlaken, you can catch such a train earlier in its route by making the short trip to Spiez. From Luzern, there is good service over the Gotthard route. The new Gotthard Basis Tunnel has taken over an hour out of the journey across (or under) the Alps. The old, Gotthard Panorama route is still in use and is a wonderful rail journey.
You are planning to visit high Alpine regions at low season. It is still the tail end of Winter, but the snow is not so good for skiing, and high trails as well as much mountain transport in the Jungfrau region only resumes service after the low season brake for maintenance ( and few travelers) on about May 25th. many but not all hotels nd restaurants are closed til late May or early June. Trails above 1500 or meters usually will be blocked by snow.
The (expensive) cograil to the Jungfraujoch runs all year, every day. I think that the transport routes to Schilthorn are open in May...check the time table starting in Lauterbrunnen or Stechelberg (or Interlaken). In mid-May, towns at lower altitudes, such as Luzern, are quite pleasant, Spring is well advanced.
The weather depends on altitude.
These links will be helpful, especially if you work down through sub-links on the main pages:
For weather and time of year, and all about traveling, work from the two menus under this main link: www.myswissalps.com/ge ttingstarted
For information about Zermatt, Interlaken, Luzern, use this page to start:
Look at the region Bernese Oberland and the cities by name. Scroll down under "Cities." Many are listed with their own pages.
Hope that helps. The timetable is a wonderful resource.