“Is there a way to collapse multiple layers and reveal them (not in the composition, but in timeline and layers windows) all at once?”
You can collapse and uncollapse in the layer list and the timeline by multi selecting the Layers you want to affect and using the left and right arrow keys.
“How about something akin to the U key in AE, which reveals all (and only) attributes with keyframes?”
I haven’t discovered a way to do that yet.