Advise 3 days in Swiss

Welcome to the forum, krissy. It would make a bit more sense to visit Wengen or Lauterbrunnen first when entering from Milan. So that would be your trip for day 1. You could do the Jungfraujoch trip on the morning of day 2 and head for Lucerne the same afternoon or evening, getting to the Titlis on day 3. Note that there are other viewing points closer to Lucerne, such as Pilatus and Stanserhorn. Visiting one of them, instead of the Titlis, would help you save on traveling time and costs. And if you'd like to include a boat ride over Lake Lucerne, you could get to the Rigi instead. If it's too hard to choose, pick Rigi, Stanserhorn or Titlis on day 3 and do the Pilatus trip on your last day in Switzerland. You should manage to get up to the Pilatus early in the morning and then catch a train to Basel. Just use the timetable to plan all trips.

As for a rail pass: yes, you'll be saving money if you buy one. The Swiss Half Fare Card is an option indeed. A 4 day Swiss (Saver) Pass is worth considering too, especially if you want to be able to adapt your plans on the spot and don't want to buy additional discounted tickets for buses, trains and boats.