How far in advance can I board my Rail Jet train in Vienna

If you have reserved seats you should have a car number and seat numbers. But, even then, sometimes if train cars are changed your car may be gone and with it your seat reservations (guess how I know)..

If a train is passing through a station it is only on the platform for maybe 10 minutes. Normally if a train originates from a station it is on the platform 10-20 minutes (sometimes more) before departure, but you cannot board it until it powers up. Find the car where your seats are supposed to be. Stand among the crowd waiting around the doors. When the train powers up the buttons at each door begin to glow. Glowing button, push button, door opens, follow crowd, find your seat, or any seats that do not have lighted labels above them.

30 minutes ahead should be enough time.

Good luck.

Vienna Hbf is the origin point of that train. Nobody is allowed to board without valid tickets/passes and reservations. If you paid for seat reservations, look for numbers, next to German words such as Wagen and Platz, or abbreviations for these.

Same as what Nick says. If you have a reservation you should have your seat details (vehicle an seat numbers). This should be on your reservation document. If it is in German, look for "Wagen" (vehicle) and "Platz" (seat).
If you don't have that, you are missing something.

The general answer is that you can get on a train once it arrives! This will be 5-10 minutes before departure in a big station like Vienna, shorter in smaller stations.
A Night Train starting from Vienna may be an exception, and if you are lucky it could be at the platform 20-30 minutes before departure.

"how early do we need to be in line for the night train NJ40233 so I can get good seats (since it is an 11 hour trip)." - again, if you have a reservation you have your seat numbers already. If you haven't got a reserved seat, what did you pay for?

There is no "line" to be in. You are not checked before getting on trains. You just get on and find your seat.You go to the platform and wait for the train to arrive.

The Eurail Global Pass - a waste of money, by the way - replaces the individual tickets, only. You must buy - for the specific train you want to go - any seat reservation separately, either online or at a counter in a railway station. If you have done that correctly, there is a designation of car and seat number on the receipt.

In western Europe there is no need to go 1st class as the rolling stock is quite modern and comfortable.

This is most likely not on your present itinerary.

If you were to go Paris-Frankfurt using the Global Pass (in either direction), a day train either the ICE or TGV, I would definitely recommend 1st class...much nicer and convenient.

You'll see quite clearly that it is not merely a matter of the seats when deciding between 1st and 2nd class.

If your confirmation does not mention the carriage (Wagen) and seat (Sitz/Platz) then I'm afraid you probably don't have reserved seats. But don't worry as the seats on this service will not be sold out so you won't have trouble finding some.