Early morning train-will we make it?

Having 6-7 minutes should be enough time in Interlaken Ost especially at 7:30 in the morning. You won’t have time for anything else but getting your luggage onto the next train but you can do it assuming you are traveling light (backpack and 1 roller bag).

Look around on some other posts about the best ways to buy tickets. Perhaps the SBB app?

What exact date are you looking at? Looks like you will be taking a replacement bus between Domodossola and Milano Centrale after June 7.

You have a lot of questions all mixed into one paragraph, so it's a bit hard to remember to answer them all. For future reference, when you have this many questions, it's helpful to break them apart from the paragraphs to help with answering everything.

First of all, yes, 7 minutes is enough if you're focused on where you're going, but if you're concerned, take an earlier option out of Murren/Gimmelwald and have extra buffer time. If you're staying in Murren, take the train to Grutschalp + cable car down to Lauterbrunnen. If you're in Gimmelwald, then the bus is your option, but you can't miss the bus stop, it's right there at the cable car station in Stechelberg. You can arrive to Interlaken Ost with 37 minutes instead if that feels less stressful to you.

Are you saying you're only going to be in Switzerland for 1.5 days total or just in Murren that amount of time?

Always buy passes/tickets directly through SBB, not third party websites. -- SBB.ch/en -- and no need to buy this far in advance, so cancelling is of no benefit. Just purchase the HFC or tickets right before you need them.

You should each have your own SBB app and purchase your own tickets so that you aren't always in charge of everyone. If you're in a hurry sometimes you can also chose to buy all on one app, but you should each have your own app regardless. You can also just buy tickets at the stations if you're confused by anything on the app. There are machines, as well as English speaking workers at a desk to help you.

No, you don't purchase tickets in advance. They don't sell out. Just get things as you go so that you can have flexibility with weather and what you feel like doing. And you don't need to be there 30 minutes prior to a train leaving. The ticket machines take a few minutes or you can just buy tickets on your phone apps in about 30 seconds.

You will save money on the on the EC train to Milan, then Freccia train to Florence with advance purchase tickets.

And if you are worried about 7 minutes at Stechelberg, you walk 50 feet from the tram exit to the bus stop. Here is a picture. You can see the tram station and the people standing under the orange sign are waiting for the bus to Lauterbrunnen station.
https://www.google.com/maps/@46.5553092,7.9017925,3a,60y,54.66h,96.96t/data=!3m8!1e1!3m6!1sAF1QipMGfgqmzKdWgDcXPBc6z52Sj1uG8XDTLKWK5t1c!2e10!3e11!6shttps:%2F%2Flh3.googleusercontent.com%2Fp%2FAF1QipMGfgqmzKdWgDcXPBc6z52Sj1uG8XDTLKWK5t1c%3Dw900-h600-k-no-pi-6.962506516580504-ya234.66082048280572-ro0-fo100!7i8192!8i4096?entry=ttu&g_ep=EgoyMDI1MDQwOC4wIKXMDSoASAFQAw%3D%3D

By the time you make it to Gimmelwald you will have had some experience with the Swiss public transit system, and will have learned that 7 minutes is generous to change trains. This is the railways trying not to waste your time.

I travel a similar route regularly (Wengen - Lauterbrunnen - Interlaken - somewhere) and I have only missed my connection in Interlaken once. That was when there were cows on the track and we ended up 45 minutes late...
I also commuted from Bern to Basel and Bern to Zurich for years. I had less then one significant delay per year...Swiss public transit is really as reliable as the people say.

And it is mass transit, so you do not need to buy tickets in advance. The only ticket I would buy in advance is the one from Gimmelwald to Florence. SBB can book that for you. But I would book it on the website, not in the app. And make an account first, before you buy anything.

Note: When will this be? In From about the second week of June the Simplon railway will be closed so you are probably better off travelling to Florence via Luzern.

Thank you all so much for your help/replies! Sounds like 7 minutes is plenty of time:) I adore cows but hope not see any on tracks that am:) I am not sure that I can reply to individual people. It's my first time on RS forum and I can't see any of the comments now that I started to reply so forgive me for not addressing individuals by 'name".

I did not realize it's better to buy the Swiss Half Fare Card on laptop/website rather than SBB app. Thank you for this tip! Will it show up in our app though or do we just show paper copy or email proof?

How far in advance would you suggest we buy our tickets from Gimmelwald to Florence?

Also, I read somewhere that you can do something along the lines of scanning ap before get on transportation and when get off in Switzerland rather than buy tickets to avoid buying ticket for the wrong destination. I forget the term but that sounds probably the easiest as long as it's obvious where to scan but we will ask for sure. I don't mean for our trip from Gimmelwald to Florence but while in Berner Oberland area,

Yes, I did find out after making this itinerary that it will take us quite a bit longer now to get to Florence due to I think construction on train track or something along those lines and we now have to take a bus from Domodosola. Thank you!

I thought we may need to buy some of the cable cars in advance (for ex to Mannlichen) but I think I am underestimating how many are on the line (not sure of correct term). Thank you for explaining we won't need to buy in advance/tickets don't sell out. That's great news:)

I can't see how to reserve our seats together on SBB app to Florence but will do some research. I'm sure we cannot reserve anything for the bus portion but hoping we can for the train from Milan to Florence. I am considering paying extra for 1st class and the flexible ticket. I have heard it's recommended on trains in Italy because it can be super crowded.

Will we receive half off our trip from Gimmelwald to Florence? Obviously Florence is not in Switzerland so I just realized I don't think we will. Should we instead buy tickets to Domodosola and then ticket from there to Florence? I'll look into the price difference next.

Thank you everyone!!! Truly truly appreciate everyone's feedback!!

I would not buy any of the cable car or mountain railway tickets in advance. There is no advantage to buying eg. the Männlichen cable car ticket in advance.
I have only one tip here though: You can by tickets for any service at any ticket office. So for example you can buy a ticket for the Männlichen cable car at the train ticket office in Lauterbrunnen or Wengen. So when you set off in the morning just get all your tickets at your first station. Unfortunately Gimmelwald does not have a ticket office. But I would suggest you stay in Mürren anyway, as there is nothing at all to do in Gimmelwald.

When you book your train tickets the SBB will put you together if you are on one booking. And you will get a reduced price for the Swiss part of the trip with your Half Fare Card.