>> We are new to Switzerland and could have planned to travel in the wrong month ... from 12-25 June.
That time should be fine if you are not planning any high-altitude hiking. Most mountain transport will have reopened after the winter closure or maintenance break.
>> We are quite confused as to whether to book our mountain train/panorama train/cable car/cogwheel train in advance ... Do advise us if it is possible to order any of these transports at the last minute. Will it be more pricey? ... Will travel to St Moritz by Glacier Express
Getting your tickets for mountain transport at the last minute is not only fine, but the best idea! You need to wait until at least the day before to see whether the weather will be suitable for your trip. Buying on the day is fine, and is what most people do. There will be no difference in price.
The Glacier Express is different though. You will definitely need to make an advance reservation for this trip, as reservations are compulsory and can sell out.
You can make reservtions here:
>> Does this itinerary make some sense to you?
Yes, that sounds like a good itinerary. Are you staying in both Wilderswil and Interlaken? Both towns are very close together, so you can be very flexible with how you arrange your excursions and activities for days 1-6, depending on how the weather turns out. Head for the peaks on the first clear day, as you never know when the next clear day will be!
As you are staying in Wilderswil, you might have time one day to have a look at an interesting covered wooden bridge there. I'll copy my text from a previous thread:
"Wilderswil itself has a lovely little nook of beautiful traditional houses, a small square with park, and a covered wooden bridge over the Lütschine River, that dates from 1738 and is just a few minutes’ walk from the station. To get there, cross the tracks at the station crossing, go down Bahnhofstrasse, continue in the same direction along Allmendstrasse to the bridge and Lütschine river (map and some photos attached)."
If you would like to see the photos, they are attached to my post of Mar 8, 2017 - 12:57 AM in the following thread: