What sections should I not skip when building the page?
The details block (who, date, time, place), a clear venue with directions, and a plain dress note cover most guest questions. Add a short FAQ for the recurring ones like arrival time and plus-ones. A page that has these four rarely needs a follow-up message, because the answers are already where a guest expects to find them.
Is the RSVP separate from the page, or part of it?
Part of it. Replies are built into the invitation rather than added afterwards, so when a guest says yes that answer is captured against their name on your list straight away, along with any meal note. You are not reconciling a message thread against the design you published.
Does the layout matter more than the design theme?
For usability, yes. Guests read invitations on phones, so a tidy vertical order that surfaces the details and keeps the reply button reachable does more work than a decorative background. Pick a look you like, but let structure decide whether the invitation actually answers anyone.
Can I collect more than just a yes or no?
Yes. As well as confirming, guests can record a meal preference or an allergy and name a companion within the limits you set, all on the same reply. That depth is why building the invitation and the reply together matters: the extra answers land in the right row instead of in a text you must remember later.