Mar 29, 2016 - 8:17 AM
All the details and how the get from A to B can be found here:
The mini fare just relates to the price. Second class offers the same level of comfort to everyone.
Interlaken is in the Jungfrau region, so you've already planned that visit. However, it's just the gate to that region. There's not much to see in Interlaken itself, so you'd better continue to Mürren or Kleine Scheidegg for example. But I doubt if you have time for that considering your wish list for the 3 days. The timetable will help you out.