4-5 week European itinerary

Taking an "overview" trip is a great idea! We did this early on in our traveling and it has served us well.
I think the time you have in each place is just fine as long as you are factoring in travel time in between your destinations. With travel, your current plan is about 40 days / 41 nights or so.

I know this isn't your order or travel but make sure to get out a map, mark out all of these places, and figure out what makes the most sense.

Use the website rome2rio.com to help you plan your method of travel between destinations and to estimate the time it will take.

We toured CERN a couple of years ago and it was just geeky-wonderful!! Make sure to make a reservation before you leave...as far in advance as you can once you know the dates you will be in Geneva. They fill up and were turning people away when we were there. They're only open on certain days and not terribly frequently.

Vienna is on the other side of Austria from Hallstatt. Best seen as an overnight on the way from Vienna to Munich. Hallstatt is nicest later afternoon, evening, and morning when the tourist crowds are thin...otherwise it's pretty overrun with people.

Your outliers are Norway and Greece, obviously. You have probably already decided to fly from Oslo to your first destination further south. When you fly home you should do so from southern Europe. Or you could travel south to north to take advantage of better weather in the south and end further north when it's starting to warm up. Norway is a cold, rainy place and the later you go, the better your chance of warmer weather.

You don't describe how you are making the connections between locations so its hard to comment on. Looks like a really long haul for my preferences. I could spend the 4 weeks in about half those places. Look at what you are skipping that would be difficult to return to a part of a future plan. For instance you are passing over Budapest which will make it difficult to return to. You are also flying past great places I Germany. Personally I would tighten it up a lot. Pick a region; say Greece to Croatia for instance where you could include Montenegro, Bosnia, Croatia and maybe up the coast to Slovenia. Then save Prague, Vienna, Budapest and one stop before or after (Munich or Transylvania) for another trip. Just my two cents.

Just for a start, I don't see how you can enjoy Venice and Positano in 5 days. It will take at least 1/2 day to get to Venice from any of your other places, most of a day to go from Venice to Positano (6 hours or more by train to Salerno, then over 2 hours by bus to Positano, plus transfer time. . . ) and another day to get from Positano to your next destination. So you'll use 3 of those 5 days just in travel and have one day to see each. No Cinque Terre, no Rome.

With that kind of a trip, you will spend a ton of money on transportation and a ton of time on trains and in airports and have very little time to see anything. Even guided tours which take you door-to-door and don't need to coordinate trains and flights do not try to cover the distances you are contemplating.

You will be spending too long travelling and not enough time actually in your destinations for my taste. One full day (2 nights in Germany) means you won't have time to see much.

As has already been stated, Greece and Norway are the outliers, particularly Greece. I would question if it is worth going all the way to Santorini for such a short time. It would make sense if you started south and worked north with the time of year you are travelling. Mid June is going to be hot in most places except for Norway.

Venice needs time. I was there last week and was surprised how busy it was and I would hate to see it in the summer.

Unless you are happy spending so long in transit, I would drop several of your locations such as Greece and Germany. The best option maybe to fly between destinations. The economy airlines such as Easyjet have had seats for May/June available for months, so their prices will only rise as time goes by. You need to pin down your itinerary ASAP and start booking travel and accommodation. Europe is going to be busier than normal, as Tunisia and Egypt are out of bounds for us and people aren't keen to visit parts of Greece and Turkey due to the migrant crisis, so other places will fill up more quickly.

"However, being young we are also planning this trip with the philosophy of seeing as much as is reasonably possible, so that when we do return we will have a better idea of where we want to revisit!"

Why make a repeat trip to see places you've seen before? Just see them the right way the first time. I have to agree with the others - what you've planned is motion, not travel.

That is a very good time of year for Croatia. Don't miss Split and an island or two (Korcula is adorable.) If it's variety you seek, then I would probably visit Switzerland, Germany and Italy with the rest of my time. That will mean less time/€ investment in traveling long distances. Fly once from Dubrovnik to one of those places and use trains or other ground transport for the rest. Spend around a week in each country. Rome itself needs a minimum of 4 days! Maybe spend just 4-5 days in pricey Switzerland and use those 2-3 days saved for an outing from Germany to Prague.

You started out by saying that the number of days allotted above would include travel time. But in each case, I'd say that you need another day specifically for the travel time from the previous region and usually most of another day for connections within a country. For instance, you would theoretically use a good part of a day to get from Cesky Krumlov to Halstatt (a direct, private shuttle van is fastest at only 3 hours; trains take 6 hours), spend one day there (that could mean one night or two), take a 4-hour train to Vienna, and spend two (or more) days there (I definitely vote for more than two).

I don't think that you will arrive at any of these places and then find that you are "not keen on" them, especially if you have already identified major sightseeing that you want to do.

Although you may fly some longer distances, see Rick's Time & Cost Map for an overview of train travel time in hours. Guidebooks will also summarize transport time between the cities covered. Lay these out on a calendar, along with the sightseeing days. For exact train schedules, How to Look Up Train Schedules and Routes Online gives you the DB train schedule link and tips for using it. For flights within Europe, try www.skyscanner.com.

Is this itinerary far too ambitious?
YES. Way too many locations and too little time spent in them and in-between them. You're going to run yourself to the ground.

My observation is that by including only a scant amount of time in outlying places like Norway, Croatia and Greece, you will be faced by further in depth trips in years to come, when you will ask yourself, "Why didn't we do this properly in the first place?"

With 5 weeks be happy with a first time 'overview' with a bit more depth...
Italy - 10 days
France - 10 days
Germany - 7 days
Switzerland or Austria - 7 days
Include Amsterdam or Prague at a pinch, but go no further.