I need some advice.

[Lobodeb]

And for party decorations, plates, etc., check out your local paper goods store. I found a place here in Chicago that primarily sells to restaurants but is open to the public. A pack of 50 plates (various colors) is only $3!

[Moesha]

I was going to suggest the matt for a photo as an item for the guests to sign. I've seen that done several times and it has always been a good idea.
Also, just another suggestion for your cake. Perhaps you could get a picture from your parents wedding and have it transferred on to a cake. We've done similiar things with other parties that we have had.