The Eurail pass is your ticket. The app will give you a QR code and it is the ticket. You'll only need to book seat reservations once.
- Paris - Strasbourg explained see above, book seat reservations on b-europe.com (link)
- Strasbourg - Basel SBB - Lucerne reservation-free. Add the train to the app before boarding and you're ready to board
- no trains in Switzerland require seat reservations. Trains run at least hourly so it's very easy to travel around the country
- 25% discount for Jungfraujoch. Book train tickets in Interlaken when you know that the weather will be good
- Lucerne - Lugano reservation-free. Choose any train you'd like, they run at least hourly
- Lugano - Milan RE train (reservation-free)
Use SBB app to get an idea of all connections available