In addition to the great recommendation that digital_pixie provided, you may want to consider welcoming a limited party for dinner, and then cordially allow for dates once the dinner is concluded. You may want to limit the "open bar" portion to the bridal party in anticipation of a larger wedding as well.

For appropriate wording, we suggest using phrases like:

"Due to limited seating, we welcome you to our wedding ceremony and dinner. We invite you and a guest to the reception following, to celebrate our union."