One aspect where an on-site conference is similar to that of a virtual event is wayfinding.
I first happened upon the concept of wayfinding in Romedi Passini's book, Wayfinding in Architecture.
Essentially, wayfinding is about letting people know where they are physically within a space and how to get where to where they want to be.
With on-site conferences, making sure attendees know where to go, what to expect to see at a venue, and know where to navigate.
When you are picking out video platforms, ticket vendors, and even the session topics, how are your attendees going to react throughout the experience? How should they interact with your virtual environment? What happens after the event?
From buying the ticket, to waiting for a speaker's session to start, to after the event is all over, think about the entire online experience for your attendee as much as you would a physical event.