Short answer yes, But please keep in mind this is a wedding so don't wear everyday clothing. Dress nice but comfortable. (ideas: jeans and a nice shirt, cute dress "not white")
No, Unless your Invite says so please don't bring a plus one. this is a kinda small feel wedding, we only what people we are close with.
Yes, if you can only stay for the ceremony that is fine. just make sure you tell us in RSVP so we know