All good questions. Keep them coming.
Here is a start.
The timetable will help a lot on journey times:
Please make sure to read the instruction page.
Combine it with this map and you can get an appreciation for the geography:
Zoom in and you can see the rail lines and the cableways:
map.search.ch/.en.html ?pos=645684,163752&z=12 8&poi=default
The menus let you display transport stops - Points of Interest/Traffic
You take the cograil from Grindelwald Grund to Kleine Scheidegg, then transfer to go up to Jungfraujoch.
Don't buy tickets until close to departure day, because of weather changeability. Night before is OK.
Do Jungfrau in the morning. You areles likely have clouds that block the views. They tend to get thicker in the afternoon.
For details about specific locations, try a search on My Swiss Alps. It won't always work, but many people have asked the same questions, and the answers are often available in the threads posted. for answers.
Here is something I found by searching for "First". Not a complete answer...
Search for Jungfrau and you can get:
That will help you understand how much time would be involved in that trip and what you can do there.