I understand that you are probably a great fishkeeper, WickedRodent, and care about your fish a lot, but I really wouldn't go with the
Goldfish. They poo so much - in 4-5 hours their little bowls would be full of poo. That would be terrible for them, and look awful on the table. If you must do fish, I think the
Guppy idea is much nicer. :) A glass bowl with some black sand, a marimo moss ball and a little
Java Fern and a bright male
Guppy would look lovely.
If you aren't having alcohol at the wedding (and I would definitely choose between alcohol and fish!) then I don't see that it would be a problem. :) As you say, you have homes lined up for them, etc.
So, I do think it would be nice with your original plan of guppies (I'd even consider Red Cherry Shrimp instead of fish!) but with poopy fish like goldies and high-end tropical fish like bettas, I wouldn't risk it. :)