A

Whatever you do make sure you set the rules. You don't have to give them anything for free! Unfortunatly some people will try to get anything and everything extra for free from you that they can. If you are offering them a free cake give them one of the flavors they originally ordered, I would offer them a 4/5" cake, simply iced. No fondant no over the top design (I would be happy to add fondant for an extra $ and upgrade your flavor for $). It's up to you but dont let the customer walk on you.

I borrowed Earlene's idea, she offers a simple, piped cake that she brings already boxed to the venue with the wedding cake (I usually end up with extra batter anyway so cost wise it won't hurt me). They recommend having a designated person add other sweets to the box for the couple to enjoy later that evening. I do the same thing with smash cakes just a tiny cake, on the day of the event (only for first birthday's).

Again neither of these are mandatory! This is what is going to work for me, you should do whatever is going to work for you.

Yes, I think whatever you do in future, be sure to set it out in black and white exactly what they'll be getting in terms of an anniversary cake, so you can point them in the direction of their original contract if they decide to start demanding major changes to the cake. It's usually just meant to be a lovely way of thanking them for their business and getting them to contact you again in 12 mths time.