Calling all seasoned travelers! I need some itinerary tips!

I think your itinerary is just fine.
If I had to give 4 days to one of these cities, it would be Rome, just like you are planning to.

Your itinerary is good. No need to change anything. Hopefully you are a good sleeper. Some people don't sleep well on night trains (including me).

I think one less day in Rome and one more day in Munich. This would give you the option for a day trip to Neuschwantstein. In Munich itself you have Nymphenberg as well as the Residenz, plus some great museums.

10,11,12 Amsterdam
13 Night Train
14,15,16 Munich
17 Night Train
18,19,20 Venice
21,22,23,24 Rome

I think it sounds really good, especially since you are arriving in evenings or early mornings. Looks like you have scheduled your travel time very well.

Never too many days IMO. As far as day trips, it depends on your interest.

Munich-You could visit Dachau, if that interest you. Or there is enough in Munich to occupy your interests.

Venice- You can wander forever,walk the back streets, eat and drink, or visit the islands, Murano, Burano, and Torcello.

Rome- There is so much to see, can take weeks. If you just want to hit the main highlights, you can do it in a few days. A day trip from Rome would be Orvieto, by train approx. 1 hr.

Your planned itinerary may be more miles than you know as distances can be deceiving in Europe.
Fly from Amsterdam to Rome on Easyjet and begin your journey north to Venice and Munich from there. You'll get so much more out of your trip.

David- If I'm taking night trains from Amsterdam to Munich and from Munich to Venice, and the train from Venice to Rome is 3 hours, wouldn't this actually give me the most out of my days there? Since the night trains won't take up any sight seeing time and will also eliminate the stress and time getting to/from the airport from where we're staying in town. I've been under the impression even if it is a quick and cheap flight, it will still take multiple hours once you add in the trips to airport, security, possible delays, and the fact that flying would also require paying for another night in a hotel. Again, this is just based on the information I've gathered, correct me if I'm wrong. Thanks!

Both night trains are German operated City Night Line services, regarded as the best in Europe, so I think you should have no trouble getting proper rest.

Based off the temporary itinerary, does it look like there would be a way to fit in Cinque Terre?

There is a possibility to squeeeeeeeeze it in ....
10,11,12 Amsterdam
13 Night Train
14,15 Munich
16 Night Train
17,18,19 Venice
20,21 Cinque Terre
22,23,24 Rome

(not sure I would be inclined however)

I like your plan just the way it is. I would not try to cram in the CT, it will eat up too much time just getting to there and from there, and if the weather isn't great or you hit a cruise ship day, it won't be terrific.

To make suggestions on activities/sights/day trips, we need to know what your interests are. There are day trips from all your cities, and plenty to enjoy in them without venturing farther afield. An alternative to a day trip from Rome would be a stop on the way from Venice. The trains go through Padua, Bologna, and Florence on the way. You could stop in any one for a visit (buying separate train tickets for each segment).

Chani's second paragraph is worth reading twice - she nailed it. With four cities and only a few days in each city, don't try to add more overnight destinations. But you certainly can take day trips if you don't like a place, or have a specific sight in mind. The beauty of daytrips is that they don't need to be planned in advance.

Since the train time is about four hours from Venice to Rome and the trains run all through the day, you can certainly stop off in a city along the way, leave your bags at the station, and then resume your journey a few hours later. As she says, you will need to plan this in advance and buy the appropriate tickets (these trains are all reserved, and you can't just hop on without having a ticket for that EXACT train, or you get a heavy fine).