Have you got any good resources which paths are recommmended, and points of interest along the way? Google doesn't seem to report much apart from a few shorter passages along the way.
Here is a map I found: https://en.eurovelo.com/ev9 This route actually didn't end at Venice as it suppose to end (and didn't pass through the Baltic states), but it is nice overview.
I have previously looked at something called the Trans Dinarica, a 2000km mountain bike trail through beautiful terrain in the Dinarica alps. Maybe this is a bit easier alternative, while no less epic.