Apr 9, 2021 - 4:04 PM
Never too early to plan a trip, that's part of the fun. My wife and I have only been there twice, and stayed in Lucerne while taking several day trips. It is very easy to do. As others have mentioned, a STP is wonderful and provides maximum flexibility in case of weather changes, or simply if you just change your mind on where or when you want to go on any given day. Or during the day for that matter. We did that several times. A Traveler's WiFI and the SBB schedule app make travel planning and changes on the fly pretty easy. We went to all five of the mountains you mentioned. Of those, Pilatus and Stanserhorn were our favorites. Pilatus because of the amenities at the top, short trails/walkways (including through the rock tunnel), and a fantastic open deck for sunny day lunches. Stanserhorn has basic amenities at the top, a nice short hike around the peak, a big deck, and of course great scenery. Plus the open air train car shuttle to the gondola provides a cow bell symphony along the way, which was actually quite relaxing. Both are close to Lucerne too.
Titlis and Schilthorn were incredibly crowded when we were there in October both years, especially the gondolas to the top. Spacing inside those was about 1.5 inches between people, if that. Although getting off at Trubsee 1/2 way up to Titlis wouldn't be bad. The gondolas to that area were not jammed and it looked like a nice place for an easy walk and/or picnic. Rigi was our least favorite. In our opinion, it was actually pretty boring at the top, but it did offer multiple stops along the way.
If you do venture over towards Schilthorn, one item to consider is doing the Grannie's Walk from Mannlichen to Kleine Scheidegg, An easy walk, plus you can have an outdoor lunch at the KS train station while looking at the Eiger, Monch, and Jungfrau directly in front of you. There are numerous posts here on MSA about the Grannie's Walk.
All the principal peaks in Switzerland seem to have mountaintop web cams so you can check the weather before heading out. Just because it might be drizzly in Lucerne doesn't mean the sun isn't shining at the top of Pilatus.
If you need to fill in a day, a quick trip to Zurich to explore the Old Town section might be enjoyable; it is very close to the train station. Or take a boat ride on Lake Lucerne; boats are frequent, plenty of stops, and the boat dock is directly in front of the train station.
Have fun planning!