Two months in advance is awfully late to be booking your venue and lining up guests of honor.
If your offer sounds too good to be true, then expect it to be greeted with suspicion and work extra hard to explain why it isn’t too good to be true.
Don’t expect prospective guests to research you to figure out that you’re legit.
Understand that even if you’re offering airfare, hotel, and food, the guests are still sacrificing time to attend the convention. They need some assurance that the time spent will be worthwhile.
Attendees will not appear out of nowhere waving money and begging to attend. You must advertise for months or years in advance to create awareness that your convention exists.
If a guest expresses interest in accepting your offer, this does not constitute an agreement, nor does it give you permission to announce the guest as attending as a lure to other potential guests.
You may have a beautiful vision, but others will not jump on board unless you can convince them that you can really make it happen.