Car or Train for this itinerary

What ever you want to do. I just recall the words off a Wengen local (WengenK), "No plan survives contact with Swiss weather."

When I need a car for a day trip when public transport does not work well, I rent it for a day.

The Lauterbrunnen parking garage will run about 80 CHF for 6 days. You could also use the Wilderswil Park & Ride at 5 CHF per day.

What time of year is this for? Renting a car for a day isn't as simple as you think. You'd have to go to Interlaken, walk 15 minutes from the train station to rent and then waste the time returning it. Stoos Ridge Hike is very much instagram overhyped. If you're staying in Wengen and it's the summer, do the Panoramaweg Oberberghorn Daube ridge hike from Schynige Platte. It's prettier and way more convenient to Wengen.

You're trying to do too many day trips from Wengen and you're going to spend a ton of time traveling. If you insist on doing Stoos and Luzern like your original plan, then you need to stay in Luzern for a couple nights to accomplish that, otherwise you're doing way too much back and forth, even with a car.

I'd recommend something like this (you have to go with the weather, but you get the idea):

Day 1 - Wengen
Day 2 - Schynige Platte ridge hike
Day 3 - Murren/Schilthorn/Lauterbrunnen Valley + paragliding from Murren
Day 4 - Mannlichen to Kleine Scheidegg + Eiger Express to Grindelwald
Day 5 - Buffer day for the activities above (you won't have 5 perfect weather days and you'll come across things you want to add while you're there exploring)
Day 6 - Travel to Milan

Thank you both! Wanderweg, I think I'm going to do exactly this, great advice, thank you!

hey hey josh
you have gotten great advice with your travels and itinerary. can't help at all since i've only been to geneva for 2 nights then on to annecy france.
some advice and tips for you to check out. things have changed in countries about renting and driving a rental car.
AAA.com/IDP all drivers will need one and can apply online or stop at a AAA and get it that day. good for a year
switzerland requires a vignette/sticker in window. check the cost if any to pick up one city and return to another. also very important is picking up in switzerland and returning to italy is a $$$$$ fine. drop off car near border, take train into italy and pick up another car
it is mandatory to have an IDP for italy. same thing about picking up in one city and returning to milan could be a fee. you need to do the legwork of which rental car company you wish to use.
parking can be expensive, price of gas, make sure to keep your voucher/ticket you get through machine thank god we had in middle compartment driving from venice to lake garda bardolino. slide it in and pay the toll.
as others have mentioned you are doing a lot of driving, looking at maps/guides saying may take 1-2 hours could end up being more, expect the unexpected.
if flying and fight says 2 hours, you have to take in the time to pack up, check out, return car, check in for flight 2 hours ahead, waiting in lines, just like flying within the USA. happy travels and enjoy
aloha