The whole value sits in the reply
A page is pleasant; a reply is useful. What makes a wedding website worth sending is that the yes arrives as a tidy record against a name, not as a message you must decode and copy into a list yourself. So design everything around making that confirmation effortless and complete.
Effortless means a guest can do it on a phone, one-handed, on a bus. Complete means the answer captures everything you genuinely need, so you are never following up to ask who is with them or whether they can eat the fish.