Cameron White

RBD Material Fracture is a higher-level wrapper around Voronoi and/or Boolean Fracture, depending on the material type and settings. Voronoi and Boolean Fracture are more low-level tools in comparison, and you may want to use them for building custom tools, etc or if you don't need the extra features that material fracture provides

If you just want to use specific cell points (for Voronoi) or cutting planes (for Boolean), RBD Material Fracture can be configured to use them, which allows you to have more custom fracturing while still having proxy geometry, constraints, etc still handled for you.
For custom Voronoi-style fracturing you can use the Concrete material and provide your own cell points via the fourth input, and disable the volume-based scattering
For custom boolean fracturing you can use the new Custom material type in H18, and provide your cutter geometry in the fourth input.

Yes, if the agent has any blendshape channels defined on its rig, you can use e.g. https://www.sidefx.com/docs/houdini18.0/vex/functions/setagentchannelvalue.html [www.sidefx.com] to override the channel values from the source animation clip.

Have you checked the bounding boxes of your agents? (e.g. turning on Primitive Hulls in the viewport display options, or looking for bbox-related messages in the Mantra output)
See https://www.sidefx.com/docs/houdini18.0/crowds/agents.html#boundingbox [www.sidefx.com] for more details, but some solutions are increasing the bounds scale or adjusting the collision layer if one exists