For the first two things they suggest:
If your site accepts file uploads, it is strongly advised that you
limit these uploads in your Web server configuration to a reasonable
size in order to prevent denial of service (DOS) attacks. In Apache,
this can be easily set using the LimitRequestBody directive.
We already have the equivalent nginx configuration in-place, so you don't need to worry about that.
If you are serving your own static files, be sure that handlers like
Apache’s mod_php, which would execute static files as code, are
disabled. You don’t want users to be able to execute arbitrary code by
uploading and requesting a specially crafted file.
If you're using the "Static files" table on the "Web" tab to set up your static files, that is also in-place and working.
The other item -- to do with validating user-uploaded content carefully and perhaps serving it from a different domain -- is something you'd need to implement yourself, as the implementation would be very specific to the way your site works -- like they say, there's no general solution.