You asked about travelling on trains using a rail pass in Switzerland. I spent a memorable week criss-crossing Switzerland on their train system several years ago. So here is my 2 cents worth of opinion on a couple of your questions.

1. Would 1st class be less crowded? Are there any reason why one may want to go 1st class (as opposed to 2nd class) on this system?

The main difference that I noticed is that you will meet interesting fellow travellers in 2nd class on intercity trains. You will see (but rarely be able to engage in conversation) well-heeled business people with cell phones and lap tops in 1st class. 2nd class vs. 1st class was not nearly as important to me as being on a NON SMOKING car.

3. Is there any need to book seat reservations on Swiss Rail?

The only time I needed a seat reservation was for the Glacier Express from Zermatt to St. Moritz. Reservations are mandatory on this train. Otherwise, I just boarded my train of choice and always found a seat. By the way, there are not enough superlatives in the English language to describe the scenery on the Glacier Express. It is a visual and engineering marvel. You go over and through the heart of the Swiss Alps - through something like 90 tunnels and over 190 bridges. If you are in Switzerland for a month, you really should find the time to make this memorable trip. It was a highlight for me.

Regards, Mark Los Angeles, CA