Activity for Rachel

So my wedding is in a castle so naturally the wedding is very formal... for my rehearsal dinner ( in April) what is the etiquette? I found this gorgeous light gold Long dress... is it to formal?

Anyone wearing the allure c380 dress??? Trying to find a sash belt that's not crazy expensive and I found one I really like but was 800 dollars! Plus the lady wouldn't give me the name since I wasn't buying it there