Itinerary looks kind of busy. For one thing, once you return from an excursion to a mountain, you may find not enough time before the trains or the cable cars stop running for the day, usually the cable cars go up until 4:30 or 5 PM.
Also, double check that if you're going in late September, some of the services may shut down in the second half of September.
I bought the Berner Overland pass on some trips. You have to be fortunate with the weather. I remember one 5 day stay, there was sunshine for a day and a half. So it got sunny on my last day and I set out to go up to Brienzer Rothorn, on the cogwheel train.
The place was packed when I arrived at the train station at lake level, because there was a lot of pent up demand from other travelers who waited for the rain to stop. I think they ran an extra train off schedule to handle the demand.
It was spectacular up there but about an hour after I arrived, which was between noon and 1 PM, the clouds started to roll in and you couldn't see Brienzersee below any more.
In fact that's what I find about Jungfrau, the last couple of times, I couldn't go up because it clouded over by late morning or early afternoon. So unless you set out early in the morning, it wouldn't be worth going up.
Same is true of Schilthorn. The one time I went up to Schynige Platte the trains were packed, I think there was a one waiting to board as trains become available.
So the amount of ground you can cover may be limited.
I've stayed in both Wengen and Grindlewald. They're nice but if you want to see other places near the lakes, staying in Interlaken saves you some time because there are transport links for everything.
So besides Rothorn, I liked Niederhorn, Niesen and Oeschinensee. I've been up to Harder Kulm more than once as well.
