As for #4 this depends on what process you use. For normal SMD reflow and THT wave you want to preferably have all components on same ("top") side. For singlepass wave soldering of both SMD and THT components you want the SMD parts on the bottom side, but such process is usually only worthwhile for very high volume (and usually single layer) boards and requires special board design.
Sure, but even just hobby stencil, reflow or pnp you might want to consider this. In this case you also have the plate which will block anything on the top once the switches are soldered.
