You are going to get a lot of people telling you that this itinerary has too many locations that are too scattered about. I'm one of them.
Do check the rail and itinerary resources already listed. Those will give you an idea of how faaaaar apart many of these locations are and how long it will take to go between some of them. If you stick to this, you will need to fly...a lot. That will add costs and travel time. At least on a train you can see something of the countryside that you are going through. When flying, you have the same security issues as back home, the same requirements to get to the airport early, etc. And you see nothing along the way.
If you haven't bought your airline tickets yet, you might want to reconsider Greece. Do the online looking yourself. The only nonstop flight I see goes to NYC. Google Flights is a good source to get an idea of what's possible for multi-city flights from home to Europe and from Europe to home. Don't be seduced by super cheap flights like those on Aeroflot or Ukraine airlines. Those often have overnight stops in their home countries.
Google Flights also works for any internal European flights you want or need to take. Keep in mind that European airlines are cheap but much more restrictive on the sizes of luggage allowed both in the cabin and checked. And they do like to add costs on to those cheap fares.
The advice here usually is to pack light and carry-on as much as possible. That means you do not pack for a 6-week trip. You pack for a week or less and do laundry in the room or at a laundromat. You can also get it done at laundries where you drop it off and pick it up later. With your rushed list of places and short times there, you have very little time to take a breath and do laundry. Packing light and doing laundry sounds like a pain, but lugging a big bag on and off trains, trying to make connections is not the way to go.
Trip planning is an iterative process. Sometimes we can't go exactly where we want to exactly when we want to for any number of reasons. It's usually a teetering balance among money, time, and what we want to see and do in the places we go. Add in traveling in high season to lots of destinations, and it becomes even more complicated. I'm not sure travel agents are very useful any more for custom trips like the one you are planning. You need to do this yourself.
The main outlier I see on your itinerary is Greece. I'm not as negative about Santorini as others. It is beautiful. But I think you would do better to take those days and add them in to some of your other locations, giving you time to rest along the way instead of only at the end.