I have an unused receptacle in the ceiling that used to have a fan attached. Now the wires are dangling out of the box (all are wire nutted to keep separate except the ground). If I go to and get a cap, how do I ensure the wires are safe to stuff in there? I don't see any exposed wire except the ground which is all exposed. Do/should I tape that?
You can leave the ground wire bare, it's fine. As long as the other wires are capped off so that no bare metal is exposed, then those are fine, too. You can bend the wires and stuff them all into the box, then put a blank faceplate on the box. You cannot cover the box with sheetrock or anything. You have to leave it accessible.
Cap the wires (done) and simply fold them into the box. Obtain the cover plate of your choice at the nearest home center.
Electrical codes to not permit permanent covering of junction boxes, but there's a qualifier: if the circuit is disconnected at the panel (wires detached from breaker) then it doesn't count as a circuit anymore. But it is unlikely that a ceiling light has a dedicated circuit.
You can cover the nasty-looking blank plate with a ceiling vent to make it disappear. By "disappear" I don't mean you can't see it, but it looks "normal". We expect vents in ceilings, we don't expect electrical cover plates. Same with switches - a blank plate in the wall says "something is out of place", a switch that doesn't do anything appears normal.