It's a great idea to get a personal app made for your wedding. I've some brief ideas for the app which I'm listing below:
In the home page you can have a beautiful pic of the bride and groom welcoming people to join the occasion with their thoughts and blessings. You may also mention the name of the parents, venue, date of the wedding etc. in this page. Then there could be multiple topics in the menu like the schedule for various events like engagement, reception, wedding etc. You can also put up the dresses that'll be worn : )
I have another brilliant idea. You can put a section of wedding photos in your app. I know wedding photos will be available only after the wedding but you can always put an update. For that another build needs to be created and you know what? I'll do it for you(if you accept my bid of course :p), I can build the app with the wedding photos included and provide you the updated app. You can consider this proposal and get back to me if interested.
Thanks anyway and yeah, best wishes on your wedding!