What Web content can and should be served dynamically vs staticly?

Until recently I've been using WordPress for my nonprofit's website, but have noticed most my site's content is fairly static (I think), and would probably benefit from being served as a static page instead of having to retrieve data from a Sql database. (Yah I use a caching plugin, but those things are notoriously complicated to set up and manage things like expiration and recaching). Which got me thinking... Theoretically, what parts of my site actually need to be 'dynamic' to run? And more importantly would there actually be a speed benefit from converting the pages that don't have to be dynamic from wordpress to regular html? (Note: I'm ignoring the time it would take to convert dynamic files into static ones, just focusing on the visitor's experience). Eg. -Things like a home or about page, with their headers and footers and jquery and CSS design - could in theory be static. -Blog posts could also be static and even a list of new posts and snippets could be generated off the server and converted to a static page. -User facing options - creating events, a donation form, purchasing items with limited inventory - do these all have to be dynamic? If they're embedded into the page then does the whole page slow down from the dynamic request, or can just that section (eg a login modal) be run dynamically.