Yes, it’s best to copy existing cards as a different object, change their type, width, etc.—which is good practice (and quite convenient) when you want to create, for example, a male character with hair and facial hair. That way, you have the same material on several objects, but with a different hair type selected from the atlas.

The “Sampling” section allows you to set the geometry density along the hair uniformly for all cards (each card has, for example, 10 intersections), or based on its length (shorter hair has less geometry, longer hair has more). The add-on handles dense geometry well, but with an extreme number of hairs, I recommend reducing their density using the built-in “Interpolate Hair Curves” asset before applying RapidHair Cards and adjusting the density accordingly—this is a non-destructive solution. You can also use the density brush in sculpt hair curves mode.

You rather need to convert cards to mesh, than apply modifiers, because for Blender applying "meshing" modifier to curves will not work. Go to Object>Convert>Mesh.

It's best to use “Convert to mesh.” The mesh has a UV map and basic vertex colors that are useful for further processing.

This is a small but very useful tool for modifying selected hair in “edit” and “sculpt” modes. It changes the density of the points on the hair and trims the selected hair.

You can adjust the strength of the normal map and the flow map directly within the material.

Yes, but it has to be consistent with the atlas/UV.

Cards are automatically rotated relative to the surface of their parent object; “fixed tilt” applies rotation only along the root's tangent, which is useful for preventing hair from bending, for example, near the ears. “Random tilt,” on the other hand, changes the tilt of the cards randomly along a curve.

Yes, you can achieve good results by combining the add-on with existing hair asset sets—or even without any add-ons.

We need a model that has a UV map, and we need to assign curves to it (the new hair system). The hair is automatically parented to the mesh; then, in the side panel (“N” panel), select the ‘RapidHair’ option and choose “Add RapidHair Cards.”

The add-on works on curves; it will be inactive on a mesh.

Version 5.0 or higher is best, but it also works in version 4.5—unfortunately, without the option to select curve types.