ETIAS - the upcoming entry requirements for US Citizens to enter the EU has been DELAYED until 2026, therefore should not have any special needs to enter the EU. https://travel-europe.europa.eu/etias/what-etias_en

Most applications are processed within minutes. It is possible however that your application may take longer to process. If so, you will receive a decision within four days. Please note that this period could be extended by up to 14 days if you are requested to provide additional information or documentation, or up to 30 days if you are invited to an interview. This is why you should apply for an ETIAS travel authorisation well in advance of your planned journey.

https://keytopoland.com/post/how-to-survive-a-polish-wedding

Gdansk Lech Walesa Airport, GDN. The airport is located approx. 1 hour from the venue by car.

The Venue is located on the lake. Although the wedding day itself will be mostly located inside, you should plan on bringing something to throw on in the evening in case you decide to go for a stroll around the lake or choose to sit around in the garden. We will have the entire venue to ourselves across the 2 days, and given Polish weddings are very long and at times a bit tiring you are encouraged to walk around and enjoy what the resort has to offer between meals and the partying. Beware of the mosquito's! Since we are on the lake you can expect there will be mosquito's. Fear not we will provide mosquito repellent.

Figuring out what to wear to a wedding especially when it comes to shoes can daunting, so here is a short video showcasing the grounds so you can plan accordingly. In case you dont watch the video, in short, all types of shoes will work fine. Heels, kitten heels, flats, etc.