If we purchase a gift certificate, are there any restrictions> And is there an expiration or time frame it has to be used?

No.

No restrictions and within 12 months

A Gift Certificate, and it will say right on the top of it, does not have an expiration date and there are no black out dates, for use. As long as there is space available on the day you wish to travel, you can go. Just use your certificate as "payment" on your online booking.

No, you have one year to use from date of purchase