<<"Your obviously a very knowledgeable person in this area and have a passion for sharing that knowledge. Without people like you these boards wouldn't be the sought after resource that they are. So, thanks again.">>
You are more than welcome. Glad I could help. Switzerland and its citizens have been good to me, and I like to return the favor. And, the country offers a lot, not just highly photographable scenery, but some interesting lessons on how to hold a multicultural country together, especially as you dig into how it works. "Direct Democracy" is alive and well.
And, as far as this forum is concerned, you will find several forum members who have detailed knowledge available on particular subjects. One of the most outstanding contributions comes from Kim -
<<"We're also following your advice and kind of take as it goes to see what might be could for any particular day. ">>
The day by day advice works for all of Switzerland, because you can look at the weather on the TV (SF1) in the early AM, and take a train to a sunny area, if your first choice is rainy. There are substantial regional differences in weather, and there are microclimates near the mountains. As it pertains in particular to the Jungfrau region, that is important. The mountains influence the weather, and it often changes quickly. The reason you go there is the high alpine scenery, so, while Luzern works better on a sunny day, it is not a failure on a cloudy day. The top of the Jungfrau is rather disappointing in low visibility weather. Down in the LauterbrunnenValley is still OK, but better in the sunshine..
If you spend a lot of money to go up to the Jungfraujoch, and end up inside clouds, it is not only a disappointment, it is an expensive one. That leads to the existence of an extensive network of information on the topic....not just weather sites on the internet.
Your hotel probably will know where to call even if you are in Luzern. The tourist office by track #1 in Luzern is a marvel of knowledge resources. Nearer the Bernese Oberland, the train stations and tourist offices in towns like Interlaken, Wengen, Lauterbrunnen, etc. often have webcams, bulletin boards, and knowledgeable desk clerks. Towns have websites with weather.
<<"We'll also try to get Wilhelm Tell journey in. Sounds like fun. ">>
Arno provided some links on the Wilhelm Tell route.
To amplify my comments on segments that can be done as individual trips, here are a few more thoughts.
The train route over the Gotthard pass is way up on the list of the world's best....particularly because of the engineering and the way it lets you see the scenery....natural and man made. Although taking the route all the way south to Lugano or Locarno ( Locarno is much preferred for a short stop of an hour or two in my opinion) is conventional, you can short circuit the end and save time by going as far as Bellinzona then turning around.
Look at the pictures here.
The train station in Locarno is a very short walk from the lakefront promenade, and from the funicular up to the Madonna del Sasso. Lugano station is above the city and a bit further from the lakeshore. So, it rewards a longer stay.
As far as the Lake Lucerne part....der Vierwaldstättersee...the lake has different parts with different characteristics. Nearby mountains can be high ( Pilatus) or not so high ( the Rigi.) Rigi will be snow- free (mostly) in May, and has nice walking available. It has more usable surface area than steep, mountainous Pilatus. The northern part of the lake is quite attractive, with nice scenery on the surrounding shores.
The southernmost part, near/in Canton Uri is called der Urnersee. It is more dramatic.
I don't have images on this laptop (traveling) but this link gives some partial idea:
In particular, there is panoramic map of the Urnersee.
For the southern part, the train at Brunnen is a good access point, and also at Flüelen, at the southernmost tip. Flüelen is sort of the beginning of the Gotthard pass. The train station at Brunnen is a 5-10 minute walk from the boat dock. Most all of the northern landing points have bus service, some have train service, such as Alpnachstad at the foot of Pilatus.
You can break (and shorten) the trip on the lake by taking a train to/from Luzern at Flüelen or Brunnen. If you take the full boat routing from Luzern to Flüelen, as part of the southbound Wilhelm Tell Express, you might consider your return to Luzern via train instead of boat from Flüelen. Saves some hours. Lake boat schedules are less frequent than train schedules, which becomes important late in the day.
Hope that helps.