Hi Karen,
I’d suggest aiming for a recording about the same length as the webinar presentations, 20 minutes. But there is no real policing here! It should be something that stands on its own for someone watching independently.
Rather than putting in a link to your YouTube, put the URL on a blank line and press return- it should embed the video just like it does in WordPress. See some examples here, many other sites can embed themselves nicely
You can upload images to put in the body of a reply as well as PDFs. Slides could be uploaded as PDF or embedded from Slideshare, or linked to Google Slides. If it were me, I would provide some links for references, and maybe some questions, thoughts to stimulate discussion.
I’m happy to give some feedback, it’s your writing space to provide more context to the presentation abstract.