extensive sound library expression maps vs. just using Note Performer (opinions sought!)

You certainly should be able to do much more than before in Dorico 3.5, though only you can be the judge of whether it’s enough for your own needs. One of the new additions to Expression Maps is that they can switch between short and long samples automatically, based on the note length and tempo. This addition alone opens up the range of articulations that can automatically be accessed. There isn’t yet the ability to have switches conditional on dynamics (so you can automatically drive pp vs ff variants of an articulation), but we hope to extend the Expression Map conditions in that direction in the future.

Another addition which I think is valuable for the workflow you describe is that you can see the basic dynamic profile in the Dynamic Automation lane, and that’s populated directly from the score. You can see p/f dynamics, as well as sfz and fp, and these also have editable envelopes. However, in 3.5 you can also see the actual CC values that will be output in the CC Dynamic Lane, so you can see the effect of the edits you make to the dynamic lane. You can draw or record CC automation over a region of the CC lane to override it just in that area but keep the automatic behaviour everywhere else.

The Dorico model is to try to represent and edit things at a higher musical level first (the Dynamic lane), whilst showing you what it maps to at a lower level and giving you the ability to override it (ie the CC1/11 lane).