April 14th, but if you know you are definitely coming sooner than that, it doesn't hurt to RSVP earlier!
Either! We know some people prefer the physical card to send and for others its easier just to go on and do it online. You can do both if you want, as well.
Semi-formal or dressy casual. It is all outdoors so dress accordingly!
It will be indicated on invitation. "We reserved __ seats in your honor"