And I'm done, phew! I can't say it went perfectly, but we got enough of what we wanted, including Sci-Fi and Space. The biggest issue is that I tried to book on my phone right at 6 and kept getting error messages, but fortunately switched to my computer at 6:06 and then everything was fine.
Here's what we ended up with ...
4/21: Liberty Tree, 6:10
4/22: Garden Grill, 11:50
4/23: Oga's, 10:00; Sci-Fi, 11:45 (I'm going to try to switch Oga's to Tuesday 4/19, we'll see if it works!)
4/24: Space 220 Lounge, 4:30
Thanks for the tips and good wishes, and I hope you're able to find more of what you wanted as time goes on, Roscoe18! I'm about to try the Touring Plans reservation finder for the first time myself to see if I can switch the Oga's day and time ...