Use Blender 4.3 or newer.

Install like any other addon. Drag the .zip right into Blender and hit ok.

This is an Eevee only effect.

The shader has no lag. The lineart component however can be very expensive for super large or very complicated surfaces. Biggest contributors is the total polycount and surface area. For huge surfaces (like a ceiling) consider using only the shader - otherwise you will spawn millions of lines. You can lighten the load by not using a light source, keeping the quality level at 0 or 1, and being careful with the density value.

Yes, but I'd be careful. Separate out large surfaces (that would spawn millions of lines) and super detailed meshes and see which you can get away with only applying the shader. It's best to build up slowly instead of slapping it onto a scene collection. Biggest speedups will come from lowering the polycount and disabling the light source option before applying.

Yes. You can use both the shader/lineart or just one if you want. Target objects can be given a transparent bsdf.

Make sure you have a camera object - lineart is spawned only inside the camera's view.

Either subdivide the target objects or increase the quality slider.