Good question. English often uses the future tense where Dutch would use the present simple. The verb "worden" usually means to become, but in this case it's best to translate it as "will be" or "will become". After all, it's clear from the Dutch sentence that the wedding has not started yet: it's in the future.
So if i were to speak in past tense, would it just be Onze bruiloft was een groot feest? Or would there be another word for was? Or am i just completely wrong?