Few Train Questions

I've pretty much decided on the Swiss Saver Pass for my family. Few questions on this:

1)I can order from the US before we go, do I have to or can I get it in Switzerland?
2)I want to go to the Jungfraughjoch - do you need reservations for this in the summer, or do they even have reservations for this?
3)I want to do the Golden Pass one day - Is this covered by the pass? I think the only thing I need to do is get reservations for our seats, correct? Can I do that from the US as that journey comes up pretty quick in our trip and I'm concerned seats will be filled.
4)Silly question, BUT... With this pass, I can get on/off as many times per day as I'd like to, correct? For example, we take a train to Interlaken, decide to go on to Brienz, then decide to go on to where ever...

Thanks

Hi Cynthia, welcome to the forum! As for your questions:

1) You can purchase the pass online or in Switzerland. Currently, an online purchase is cheaper though. To order, and to see all purchase options, please visit the Swiss Pass page.
2) There are some trains that allow individual travelers to book seats (only groups can pre-book for any train) for the Jungfraujoch train, but it is not necesssary to do so. There are plenty of trains.
3) Yes, the Golden Pass route is covered by the Swiss Saver Pass. Seat reservations can be arranged for online.
4) Yes, you can travel on as many trains as you like. There's no maximum number of trains, milage or time limit.

I hope this helps. Enjoy your stay!