Do I use shampoo or soap on my scalp?
probably just soap.
I never bother washing my shaved head as every other day I shave it and the shaving soap pretty much does the trick. 
Ive heard the best thing to use is Johnson’s Baby Shampoo or Oil (Can’t remember which)
Shiny…
I use soap. But like Seven said, shaving it every other day pretty much cleans it. You’ll notice that your blade picks up some white stuff as well. That’s dead skin. Shaving=exfoliation!
You can also find some good info here.