Best after resting: let the harissa chill for a few hours (or overnight) so flavors meld.
Heat varies by chilies: older dried peppers are usually milder; adjust cayenne accordingly.
Storage: keep refrigerated in a jar; a thin olive-oil cap helps prevent drying and can extend freshness.
Freezing: portion into an ice cube tray, freeze, then store cubes in a freezer bag for quick use.