<Also Ive read that its better not to purchase the tickets to Jungfrau ahead of time because the weather can be unpredictable...is this correct? We will be in Switzerland first week of May.">>
Absolutely correct. All of the manned train stations and the various tourist offices will have up to date advice on the weather "up top." It is good to schedule a couple of days in the area as you have done...the weather can change rapidly.
May is still winter above 2000 meters., but skiing is thinning out, so many ski lifts may run sporadically in May and will resume for "Summer" service in mid to early June. May is usually very nice at lower altitudes.
The cograil to Jungfrau and Jungfraujoch runs all year round.
If you spend time in Switzerland, especially during the changing seasons, you learn to pay attention to altitude.
The forum moderators, Arno and Annika are the experts on rail passes. I always leave those details up to them.
However, this may help you get started:
A couple of good maps are:
and, for more in depth information, try:
map.geo.admin.ch/?topic=swisstopo&lang=e n&bgLayer=ch.swisstopo .pixelkarte-farbe&X=163050.00&Y=63 8250.00&zoom=4&layers= ch.swisstopo.swissalti 3d-reliefschattierung&lay ers_opacity=0.6&layers _visibility=false
or, the home page at :
www.swisstopo.admin.ch /internet/swisstopo/en /home.html
and explore the menus.
It looks like you have a nice trip planned.
Unless your departure from Zürich is very early in the day, you may also consider staying in Luzern, and taking one of the two per hour trains to Zürich Airport.. One hour trip. 45 minutes to Zürich, at least twice per hour.
However, a day trip from Zürich works well, too.