Having quite a bit of experience with this. Rome, Milano, Venice, Düsseldorf, Hamburg, Berlin, Warsaw, Zürich, Livorno, Firenze and in Austria you have Bregenz/Feldkirch.
A lot of these will have longer stops for example in Salzburg depending on the train 0.5-2 hours. (Mostly around 1-3am).
And like its been said already you have Seeats (6per compartement), Couchettes (4 or 6 per compartement) and sleeper cabins (1, 2 or 3 per compartement) and sleeper deluxe (with a toilet and shower. The earlier you book (usually) the cheaper the prices. Like already mentioned theres a special offer called "Sparschiene" which is a limited amount of tickets (altough available online/ via tlephone booking or at any oebb tourism center or info desk). Btw online and telephone bokking have two different price pools so a ticket may be cheaper online than on the phone or the other way around (always good to check both).
Personally I only travled in a sleeper cabin because I feel like even though it sounds pricey do consider that its basically a train ticket + a hotel room ( so the price and quality matches a mediocre hotel imo) and the sleeper cabins do have actual feather blankets and pillows and an actual matress while the couchette only offers a well um couch like "bed" and personally I feel like couchettes are just really cramped. (I also heard that theres been problems with people stealing stuff in the couchettes but that was mainly in the summer time and in italy I think)
Oh also theres not really a good "dinner" option on the trains so you should eat before you board the train but depending on the train it should be fine since they leave between 19:00-23:00 depending on the train!
And a tip might be to look into interrail/ eurrail tickets. Theres an option for a one county/global pass depending on how much you plan to travel by train. So maybe look into that, just keep in mind that with night trains the pass only ever covers the traveling cost but not the reservation for a seat/etc.
Another tip might be to check out Oebb railtours as they offer some combi-tickets that include hotels/entrance tickets for events and stuff like that.
Sorry for long post!