We have found that you should include signature lines for about 75% of the number of guests that you expect. It is not necessary to include signature lines for everyone, since couples will sign together.
You should lay the document on a large flat table in a relatively low traffic area. Your guests should sign the document left-to-right across the document. This way, at the end of the ceremony, you will not have a half-full column on the right side.
Documents and certificates are shipped rolled in a hard plastic tube. When they are received, they should be taken out and laid on a flat surface. They should uncurl themselves within a few hours. A warm iron may be used on the back of the document if needed.