Hello Sarang! I'd say you've made up a perfect travel scheme for a 5 day stay in Switzerland. It allows you to explore several towns and diverse areas, without the travel scheme being too full. Mt. Titlis, Jungfraujoch and the Golden Pass train are true highlights. A few tips for the 5th day, although I don't know how late you'll be leaving for Montreux and if you have enough time lefti the morning: you may consider a short boat trip on lake Thun or lake Brienz. A nice viewing point, which can be reached from the centre of Interlaken, is Harder Kulm
. And for a spectacular lunch or coffee break, consider the terrace on Top O'Met
. As for your 4th question: no, there are no highlights I think you should add to your itinerary. Again, it's complete and includes a lot, without requiring you to hurry.
The trip to the Jungfraujoch is expensive indeed, as it's discounted by 25%. Regional passes offering more discount are available, but they're all valid for several days and as your stay in Interlaken is short, these passes would be too expensive. There's also a Good Morning Ticket for travellers on the first two trains each day. This ticket has a reduced rate, but as it's meant especially for those who don't hold a valid rail pass, it won't be an option in your case. The reduction with your Eurail Pass would be better than the reduction of such a Good Morning Ticket. So I don't think there are alternatives. But if weather is fine, the trip up to Jungfraujoch is worth its money! It's absolutely spectacular to really be up and in between the mountains and get so close to huge snow fields and glaciers. A price overview can be found on the Jungfrau Railways website
Yes, most towns offer a guest card. The hotel personell will hand it over to you. If not, you can ask for it at the local tourist office. Guest cards don't always include free travel, but reductions on local public transport are mostly included. Please review all information on the Interlaken visitor's card
and the Lucerne guest card
(download the brochure 'Cityguide'). The Lucerne Card
(for which a small amount has to be paid) may be interesting as well. The BeoAbo
seems to be available for Swiss residents only and is valid for at least a month, so this isn't a good option for you.
I hopes this answers some of your questions!