Hello Lmyuen and Welcome to MySwissAlps,
April to early May is pretty much between the winter and summer tourist seasons in Switzerland so things may be very quiet at the tourist destinations. It is still winter at higher altitudes and just moving into spring down lower. Some cable ways and mountain trains are closed for maintenance.
Stanserhorn doesn't open until mid May, same with cog-wheel from Alpnachstad to Pilatus(though cableway will operate). Jungfraujoch and Rigi are accessible all year round.
I am a big fan of the SBB Mobile app (bit.ly/2ICIUHi) for checking train, bus, boat and cable way timetables, finding fares* and buying tickets on-line if required. In the unlikely event you don’t have a device capable of running the app then you can use the timetable on the SBB website (bit.ly/2HH1U7B). If you are not familiar with using the timetable it will pay to first read the instructions at www.myswissalps.com/ti metable.
* The SBB website shows half-fare prices by default, the mobile app allows you to nominate whether to show full or half-fares (by editing the passenger details in settings) and is also smart enough to offer you the Saver Day Pass (www.myswissalps.com/sa verdaypass) if that offers the best fare. The app can also display a platform map (at least at the larger stations) to help you make connections. You can also easily filter modes of transport (eg bus or ship).
Based on your personal itinerary you should read “How to choose the best travel pass” (www.myswissalps.com/tr ain/ticketspasses/prac tical/chooserailpass), download the handy spreadsheet calculator and do the math. The spreadsheet also includes links to the “Where it's valid" page for all available passes. Be sure to check those pages for each pass you are considering. Study the map AND read all the text on those pages to fully understand what is covered by the respective pass.
A good way to map out an itinerary is to visualise it using the Swiss Travel Pass Area of Validity map ( PDF downloadable from www.myswissalps.com/sw isstravelpass/validity). You can cover a fair bit of ground in 14 - 15 days and a 15 day Swiss Travel Pass sounds like it would be ideal for you. But don't end up moving around too much otherwise you will spend a lot of time checking in and checking out of hotels.
If you are travelling with a 2nd Class Swiss Travel Pass but want to travel 1st Class on any particular trip you can buy a Class upgrade at any SBB station or using the SBB Mobile App or here bit.ly/2rZEIXh. You need to buy a route specific upgrade.
www.myswissalps.com/tr ain/practical/2nd1stcl ass
If you buy on line you need to nominate a Half-fare Card reduction to get the correct price (using either website of SBB app). An upgrade will cost half the difference between 1st and 2nd class full-fares.
Does that help get you moving in the right direction?