You can absolutely do that. If you want to upgrade to a paid plan to get some of the features you want, then you can switch at any time through the My Products option in your account or with the help of a GoDaddy Guide. Once you upgrade your site will have all the same customizations and work that you've already put in place, just with the added features. See Website Builder plans and pricing for more info.
Having seminars on the internet has been very popular and is used by a lot of people. This is a way to connect with your audience and reach out to them even though they are miles apart. It is an effective way to actively connect with them and that’s why the webinar template is a unique feature of sales funnels. It entices your audience to join or avail of your products because of your presence and make them signup.
How to Build a Dangerously Effective Sales Funnel