We are at DLR now and I am sad to report that PFF has turned into a meet & greet/shopping only. Massive lines to meet princesses, but no show or arts and crafts or storytime!

Maybe someone knows whether those will be coming back, but for now at least, the whole stage/seating area is blocked off entirely.
Based on trip last August and this trip, Nemo subs are a good "first thing in the morning" ride. However, later in the day I have not seen the lines over 60 minutes, as opposed to the 2-3 hours(!) back when they first opened.
My DH and DS rode the Matterhorn the other day (when the park was very crowded) around 11:00 a.m. and the standby line was 45 minutes. So not too bad!
This week (spring break) and last August when we were here, DCA opens two hours later than DLR. DLR at 8, DCA at 10. However, you can walk into DCA at 9:30. Soarin' is the only ride I know of that is open before 10, but that's a great time to walk on with no wait, then zip down to TSMM when the rope drops in Sunshine Plaza at 10. If you are among the initial mob headed to TSMM at 10, you can get on with about a 10 minute wait . . . but once you get off, it will be up to 45 minutes and I haven't seen it any shorter throughout the day. Maybe late night during the electrical parade would be a better time? Unlike DHS, there is no FP for TSMM at DCA.
Riverboats are closed for refurb right now - I don't know if they will be open again by June. Tiana is doing her show on the steps in NOS. It's kind of a mini show which is nice because you can get up close!
Thanks for mentioning the Beast's Library - I have never heard of it but will now try to find it at DCA - my DD will love that!!