Doesn’t need to be real time, just secret. You send a reply to the host with your wishes until a specified deadline. The host then opens all envelopes at once and figures out the guest list. Like an election.

This would be better done without interaction, but blind voting.

Otherwise there’s no incentive to vote first. You want to save the +1 for yourself as long as possible. Which means nobody will RSVP or bring a +1.

Don’t Wedding guests give money as gift?

The high price for first Party Nintendo exclude games doest matter that much even. I buy the physical versions and the have good resale value.