Should I leave some spare cable at the patch panel and outlet?

A sensible service loop is useful. Leave enough spare to reterminate or reposition the end without having to replace the whole run, but do not leave huge coils simply because cable was left in the box.

Dress the spare so it keeps its bend radius, stays out of the way and can actually be reached later. Spare cable that has been crushed behind a cabinet is not much of a favour to the next installer.