Taking trip London, Munich, Switzerland, Italy. Best to do a Eurail pass for The bottom three and then add the London trip since Eurail does not service England or buy separate tickets London to Munich, Munich to Switzerland, Switzerland to Venice, to Florence, to Rome.
You'll probably be better off flying between London and Munich. Saves lots of time and there are numerous discount airlines to choose from: Easyjet, Air Berlin and Germanwings fly that route. The train will take a minimum of nine hours with changes. The flight about 90 minutes.
I'm going to guess that it will be cheaper to buy point to point tickets the rest of the way. In most cases, it's much less expensive to buy point to point tickets in Italy than it is to buy a railpass.