The sooner the better - just for purchasing plane tickets and making travel arrangements - but letting us know by the end of November would be wonderful!
We recommend semi-formal. The ceremony will be outside and it could be a little chilly, so plan to have a jacket. There will also be a (optional) walk through the streets afterwards (on steep cobblestone roads) so plan shoes accordingly.
Yes, feel free to bring whoever you are traveling with -- just let us know how many you will be when you make your travel plans!