G'Day Lucy -
<<"Is it easy to navigate the above itinerary.">>
I hope that was a question, because I'm going to answer it.
The answer is "yes."
Here are the concerns-
Day 4 is very long. It is easy to navigate. And, once you are there, if the weather is good, there is a chance that you'll want to spend more time there. And, if it is not, you'll wish you were there on another day.
The weather changes frequently, rapidly, and unpredictably in the high Alps. Forecasts are not much good beyond 24 hours, maybe 48 hours.
I was going to express a strong preference for more time in the Jungfrau region at the end of your trip. . Then, I remembered that you are traveling in April. I withdrew my strong preference. ;-(
So, I've gone back and edited my thoughts, because i was thinking of Summer hiking . April in the Jungfrau region is really low season. Skiing is bad...no skiers. Trails are snowed in...no hikers. Lots of tourist facilities are closed.
Check the schedule for Schilthorn...... not sure exactly when their multiweek shut down for maintenance occurs...might be April. If it is running, the Schilthorn trip might be enough time there...in April.
If it were late June or early July, my own preference would be to put a couple of days at the end of the trip staying in, for example, in Wengen ( or one of the other villages near the Jungfrau). After you have visited Pilatus, then it is a choice between a couple more mountains near Luzern (if you stay in Luzern) or the whole grand panorama of the Jungfrau region. The Rigi is a lower altitude experience and has some nice walks. Titlis is a high Alpine experience, in the same general category as the many options near the Jungfrau.
I really the region around Luzern, especially the lake. There are some nice hikes nearby, mostly accesible in the main in April (lower altitude) and visits to places like Hammetschwand add to the options. These older threads have some pictures and discuss getting to Hammetschwand before they re-opened the funicular up from the lake to Bürgenstock...now operating with a reasonably frequent direct boat to the lake station.
Not sure exactly when Hammetschwand opens.....definitely by early May. Not sure about April.
This describes a hike near the southern end of the lake, and mentions the "Swiss Path" ( der Weg der Schweiz).
So, there is plenty to do around the Lake, and the high trails in the Jungfrau region will all be blocked by snow in April.