1.) Explain it with some images, your notes are very vague in my oppinion
2.) Not with panels. Panels don't supprt shaders.
3.) Particles are part of the 3D scenery and can not interact with 2D panels. Panels are alwyays drawn above the rendered image.

If you want to achieve 2.) and 3.), you have to write a panel system that is settled in world space via e.g. sprites or quad's (meshes with two polygons, forming a rectangle).