Here's a bit of a reader's digest of various resources about hosting virtual events. I took multiple cvent webinars and they honestly cover a lot of the same ground even when the names are different. I've linked to one I found most useful below.
Marketing a virtual event
Fast Track your Virtual Events (cvent webinar, very useful)
Basic guide from Cvent on Moving to Virtual Events
Thorough guide from MPI on Moving to Virtual Events
Relevant if you use zoom is ILEA's How to Make Virtual Events HappenRelevant if using Webex: Webex Meeting Security and Webex Virtual Events (includes a comparative of their products as it relates to virtual events)