A typica l invitation package consists of the invitation itself, a cover design, a separate invitation to a reception or party, and an RSVP card and envelope.
Some invitations use a cover.
If you're considering this type of design, what kind of imagery would you want. You'll want to send the invitations out 4-6 weeks in advance of the ceremony. Printing takes 1-2 weeks. If you need to let a vendor like a caterer know how many people will be coming, it's generally a good idea to check with them before setting the RSVP date.