Europass ?

We have been to Europe 3 times,each time for months and we have always used point-to-point. Add up the cost of 2nd class tix for the journeys you plan. The Rick Steves book "Europe Through The Back Door" has a chart.
You will likely find that p2p tix are much cheaper than a pass covering the time period and number of journeys you propose.As to reservations, they are often included in ticket prices and are not always needed. Trains to popular destinations,generally overnight trains and special routes will require them but most do not.

Thanks !! Some of the trips I listed here they don't seemed to have many trains daily, for instance Venice-> Bern, and Geneva -> Cannes. would you recommend to reserve online or you can do everything at the train station on the date you travel?

Since Trenitalia doesn't accept U.S. credit cards, you won't be able to buy your Venice/Bern or Rome/Venice tickets online from them. Don't worry, you can easily buy the tickets once you get there. You can buy the Swiss tickets from www.sbb.ch/en/index.htm and the French tickets from www.tgv-europe.com.

You don't need a railpass for Italy. It will be more expensive. It appears that you have been looking at RailEurope for your P2P ticket pricing. They are a ticket broker and are more expensive. Did you also see the page on the Eurail site that shows you that Italy will charge you an additional 15E-20E on top of your pass to ride the Eurostar trains? I see 3 trips above where you will most likely be on a Eurostar. That's and extra $90 in reservation fees. Also, from Naples to Sorrento, you will be on the private Circumvesuviana train. They don't accept the Eurail pass. Neither do the ferries or SITA buses in the Sorrento/Amalfi Coast area. Also, in France, you will pay an extra supplemental fee on the TGV trains.

You've done a nice job on mapping out your travel plans. You need to look at the Italian, Swiss and Frence train sites to see the real P2P fares. It's more work but you will save money for your efforts.

"I searched the euro rail website of the following cities ..."

The schedules on the Eurail website (www.eurail.com) are very abbreviated. The schedules on the RailEurope website aren't much better. RailEurope only shows schedules for trains for which they sell P-P tickets, a very small subset of the actual trains, mostly the most expensive ones. And don't use them for price comparison, because their point-point prices are inflated.

Use the German Rail website for complete schedules all over Europe. For Venice to Bern, the daily schedule is somewhat limited by the fact that it takes at least 7 hours, but I found 7 of those faster connections for trains leaving Venice after 6 AM and arriving in Bern before midnight. If you are willing to spend more time in the train, there would be a lot more connections.

Thanks for all your help. Since we have a pretty tight scheduel, would you recommend to purchase these tickets on those website in advance, or should we consider purchase it at the ticket booth when we arrive?

You could get an Italy/France/Switzerland pass. You can combine up to 5 countries and not pay for all of Europe.
I would always go with the pass. It's less cash you have to worry about having in Europe, and less you have to "budget" for as your trip progresses. The more I can financially take care of ahead of time the less stress I have on my trip. Even if I did pay more the peace of mind would be worth it. I think it's usually a good deal though. A friend of mine ran out of money on a trip and didn't even have transportation money to get home - granted, he was a tad irresponsible but why not eliminate all worry about that and just pay in advance. Besides, who wants to spend all that time "accounting" figuring out their budget with all those train tickets. Keeping track of room and board and miscellaneous is enough for me! And worse case scenario - if your cash, cards, whatever are lost or stolen and you're broke at least you can get a train to your plane departure city.