Can we see the abbey and then do a Danube cruise in one day from Vienna using the train?
Yes, go to Oebb's website and look for the Combi ticket.
Please read the thread below called Vienna Melk Day Trip:
https://community.ricksteves.com/travel-forum/austria/vienna-melk-day-trip
Basically, take the train from Vienna to Melk, take the boat from Melk to Durnstein, take the bus from Durnstein to Krems and take the train from Krems to Vienna. Can be done in a day.
Thanks for the replies. Can this be done on a Saturday or would a weekday be better?
I think I would just go on a day that the weather is nice. All of this can be purchased day of, so no need to book in advance.
Thanks for the help!