Is there any maximum length for the webinar video?

There's no limit to webinar event length, (or size of video) that you can load to your Video Library

You can create as many webinar events or add as many videos as you like, also.

If you're running Automated webinar events, you would want to consider the number of clients you're marketing to & the time they spend at the webinar event, and estimate how that may affect at your Subscription's capacity limits.