A few questions:
1.) Is a normal +1/-1 needed for floor/ceiling distinctions (i.e. is it one sided)?
Yes. Walls are directed, i.e. all particles have to be on one side of it. The side the normal points to.
3.) Why do two normal [0 0 +/-1] wall contstraints at dist z=0 and z=10 in a 10x10x10 box give a constraint violation error for one particle which starts at the center [5 5 5]?
Because the distance to the origin (z) is measured in multiples of the normal, hence you need to put the second wall (top) at z=-10. In fact, I don't know, if it is okay to put the wall directly at the simulation box boundaries at all.