The limits on meeting participants depend on which plan you have. Here is our pricing page which lists the participant limits: Plans & Pricing for Zoom One | Zoom
The Web SDK can be used to join webinars, not start them. More info here:
As a part of our solution we use Rest API to start meetings. So, if we create a webinar under a licence that supports webinars using Rest API and then use Web SDK to join it, everything will work, won’t it?