Is there a typical reply rate I should plan for?
We would rather not invent one, because attendance depends on your guests, your date, and how clearly you asked. The honest number is the replies you have, plus the not-yet-answered you are still working to reach.
What do I do about guests who never reply?
Treat them as a range you can still shrink. Send a reminder to the non-responders from the event page; some will answer, and the list updates, so the unknown gets smaller instead of becoming a made-up percentage.
Should I count plus-ones as coming?
Count the ones who are actually named. If a guest has confirmed a companion inside your limit, that is a real extra place. Anything still unnamed is part of the open range, not a fixed addition.
Can I plan before the deadline closes?
Yes, but plan from what is confirmed and treat the outstanding names as the risk. The live count means you are always looking at the most current figure, not one you estimated weeks ago.
Does this turn into an attendance forecast for me?
It is a guest list, not a forecasting tool. It shows who has replied yes, who has not, and who is with them; how you read those against your own plans is the honest estimate, without a fabricated rate.