Passport control between Italy and Switzerland

Both Italy and Switzerland are parties to the Schengen Agreement, which allows for free movement between all countries of the agreement, so there are no border controls (Immigration) you will encounter, much like travelling between Provinces in Canada or States in the US. Switzerland is not part of the EU, so technically there may be some Customs activity, but not as it applies to the typical tourist.

All that said, sometimes police will board a train at a border and walk through checking passports, and there have been some border measures put in place from time to time in response to the refugee crisis. The other disadvantage of the Schengen Agreement is that rather than having an allowable amount of time in each country, you only have 90 days in any 180 days that you can be in the entire area combined.

Italy and Switzerland are both part of the Schengen zone, so there would be no passport control going between those countries. However, Switzerland is not a part of the customs free European Union; Italy is. So you might have a customs check when going from Italy to Switzerland, but in my experience, customs in Europe is a formality. You just say you have nothing to declare and pass through customs.

As above.

We took the Bernina Express from Switzerland to Tirano, Italy with return. The Tirano station had a customs office that everyone just walked pass, not even through a green door. We did see a poster advising that one can carry in excess of 10.000 EUR provided that a customs form be completed declaring the amount. We did not see a Swiss customs office.

All I can add is that on the RS Alpine tour (2015) we crossed the border into Switzerland from Austria by bus. Our wonderful leader, Cynthia, reminded us several times the day before and the morning we left, that our passports should be ready in case they were requested at the border. They weren't, but sometimes they are.