Spacers need to go in repelling the center magnet. It can be kind of fiddly. I don't know about degaussing, I haven't had a problem with mine but they've all been ceramics.
in theory, it could degauss the center mag, but in practice i havent seen it. as mentioned, you want the same poles facing each other so they repel so if you had the center mag and two side mags youd want the orientation to be this: