The modifier updates in real time while you change parameters, but heavy settings (small voxels / large models) may slow down viewport. Use ViewportAs > Point cloud during tweaking to keep things faster, you can also use Fast generation method for larger models and smaller voxel size.

Yes, you can enable generate static mesh and export the results as a static mesh.

Yes, but I don't recommend it. right now the colors are saved inside attributes, these attributes will be exported too, and can be accessed in your third party app. however I am currently working on a new technique as well, which will pack all the UVs into a single Color Palette Texture.

Yes. Voxify currently works with a single baked texture (e.g., diffuse color map). It does not support multiple materials assigned to different faces of the original mesh. Workaround: Bake all your materials/colors into one image texture, then assign that texture to a single material on the input object.

Viewport As controls what you see while editing, Render as controls what will be rendered. in large scenes setting the viewport as to point cloud will help optimize your viewport. (IF you are baking the nodes inside of geometry nodes for animation, etc, you will have to set the viewport to the same setting as your render.

Voxify instances cubes efficiently, but very small Voxel Size on a large mesh can generate millions of instances. Start with a larger size, then gradually decrease.