Hello @Graeme Kan
There is a timetable change on December 14th, 2025 and it is usually not possible to book early, I would say 2-3 months in advance. In November you have often a Black Friday sale and Eurail passes are cheaper, last year 25% discount. You can search other dates in the future to have an idea of the prices. Saver Tickets are more expensive during peak times (holidays).
Oei, very far ahead that you’re planning in railway terms, like @Danhiel said 2-3 months in advance is enough.
On these routes first class is rather nice, so quite worthwile to try it. I wouldn’t doubt.
If you want to get an idea of your rough itinerary just pick a random date somewhere next week, to get an indication of how long it takes to get from a to be and which services you can expect. Can help you already to book accommodation. Timetables won’t change that much in December 2025, maybe a couple of minutes.
Seat61 has some guidance on what you can expect fares to be if you search his route pages. On most routes, he shows a low price, which is the cheapest you can usually expect if you book at the perfect time, as well as the fully flexible price
For example, Salzburg to Vienna starts at €19.90 for the cheapest advance ticket, and goes up to €59.90 full price.
https://www.seat61.com/trains-and-routes/vienna-to-salzburg-by-train.htm