Eurail Passes
You said that you are not over 26. If you are UNDER 26 you are eligible for a Youth Eurail pass (OK, only 2nd class allowed but still very comfortable) & this makes a great difference to the price. You need to work out how flexible you wish to be about your travelling. If you are definite about how long you wish to spend in each city you may be able to get advance booking that are cheaper than the pass. However, if you want to be able to vary your stays in certain places you'll need to get a pass as advance bookings are for specific day AND train. So you need to plan the train trips you wish to do and see how many travel days they add up to. Then you can determine if you need a Global (unlimited) pass, a Select (flexible) pass (typically 10 or 15 days in 2 months) or whether you can commit to fixed dates this far in advance.
I'd also strongly recommend you reference Mark Smith's excellent site Seat61.com. He has very detailed information on various passes & where to buy them, & equally detailed stuff on booking & buying point to point tickets. His site will also provide access to route planners which will allow you see see how your itinerary hangs together.
Good luck
Dave