Build a website where you can display a preview of your Webflow template and sell them for a good price. There are two ways you can do this, sell each template individually and once you receive the payment you can transfer the site to their site. The other way works well when you have a lot of templates, you can create a membership site and have all the templates available for paying members. Membership functionality can be added easily with Memberstack. (the link below is an affiliate link of Memberstack)
Add Disqus for an easy way to add comments for your blog collection or any page on your site.
A forum can add value to your website especially if you have an active community behind it that not only engages with your great content but also gives them the power to interact with each other. You can add forums to your Webflow site with Discourse. Fun fact : Webflow's forum runs on Discourse.
Do you need your modal to only come up once per user? this is the tutorial you are looking for from Pixel Geek.
Create a site in Webfllow and sell your digital products, it can be ebooks, photography, digital arts, graphics, etc. You can add a small free selected product so users can get a small taste of what you sell and then offer a membership for the complete packaged. You can sell these digital products with Gumroad by adding a direct link to a Gumroad product page or if you don't want to take users away from your site you can use the Gumroad overlay or the Gumroad embed. I've added the link below showing you how to add Gumroad to you Webflow site.