Incorporating cupcakes into your centerpiece is a very interesting idea. This can be cost effective (less flowers) and functional (guests can eat dessert when they want). This is a great alternative to having cupcakes but displaying them on a stand as if it were a wedding cake......a lot of creativity between baker/designer/florist is necessary but definitely a very cute option!
Once again no mason jars, but I like the sign and if I do arrange table settings since it will be late and there is dinner then this would be cool. I love the thought of place cards but I've never actually been to a wedding with them.