I just found your post today (we booked our 3rd Alaska cruise over the weekend on Ovation for September) and I can't tell you how much I've enjoyed it. As a super planner myself (the fact that I booked a cruise 3 months out is giving me heart palpitations even if it is my 3rd Alaskan cruise) I loved reading through your thought process and just how organized you are. My internal OCD super planner (who makes the bookings, does the research, provides itineraries, does powerpoint presentations to the rest of the family/friend groups) is cheering for you and I hope that after the year you've had, you, your wife and your daughters will have a wonderful graduation as well as a smooth and successful trip. I look forward to reading your trip report!
I don't think I saw an answer with regards to your question about entrees on river cruises - but yes, you can request more than one. We did a river cruise on the Danube in September/October of 2018 through Gate 1and though the portions were European sized (uh...much smaller than our robust American appetites 😂), the chef came out and told us we could always order more. If Gate 1 (which is much more budget friendly than Viking, Avalon, or Ama) allowed for multiple entrees, I'm sure any other cruise line would allow for multiples as well.