The Berner Oberland Regional Pass covers all modes of transportation 100 %, including the cable cars, trains, ships, and buses, in all the places you mentioned except for Zurich to Lucerne*, and 1/2 price from Kleine Scheidegg up to the top of the Jungfraujoch, 1/2 price from Murren up to Schilthorn, and 1/2 price for Mount Titlis cable cars (near Lucerne). It costs 310 Swiss Francs for a 6 day pass, or 350 for an 8 day pass.You can buy it at the Lucerne Tourist Information office (Tourismus) by track 3 (your train from Zurich will pull into Luzern's track 4) for the rest of your journey (or any Tourist Office in the BO region).
*It doesn't include excursions near Lucerne like Mount Pilatus or Rigi or Lucerne Lake. The BO pass does include the train to Bern from Lauterbrunnen, however. I don't know your reason for wanting to visit Bern on this trip, but Bern isn't on the way to Lauterbrunnen if you take the gorgeous scenic route (via Brunig).
Since Lauterbrunnen, Mürren, and Gimmelwald are all in the same area, you only need to pick one for your hotel base to visit all three.
I agree that 2 nights in Luzern should be sufficient. The rest of the nights you could stay in the Lauterbrunnen area and visit Mürren, Gimmelwald, and Bern from there.