More detail here on the class web site J/30 Crew Assignments and in Bill Kneller's Rhapsody crew guide, an Excel spreadsheet that you can modify to suit your preferences.

Moveable ballast in the form of crew on the rail helps more in breeze than it hurts in light air so seven crew is a good target, though it's easy enough to sail with six. If you don't cross sheet the Genoa, match a light person for final trim with someone who is big and strong.