Only you need an account. Your vendors just open the link you send them.
The end time decides when your vendors' links stop working.
You type this once. Every vendor on this event sees it.
Leave blank if they trade under their own name.
Leave blank and they simply aren't measured on arrival — nobody is marked late against a time they were never given.
Your standing rules. A caterer and a DJ both see these.
Things only your DJs need, or only your caterers.
Separate with commas. What they tell you they cover.