How to make Safari remember zoom level per site?
Yes,

There is an extension for this called ZoomBySite. Here is a description of the software from it's website:


  ZoomBySite is a Safari Extension that will automatically zoom each
  site to the zoom level of your last visit to the site. A site is
  defined by a unique domain name (so www.apple.com is considered
  different from store.apple.com and each could have its own unique zoom
  level).
  
  It does this by intercepting the Zoom In and Zoom Out keyboard
  shortcuts [...]. It zooms the page in or out by
  the desired amount (see the Preferences section below) and also stores
  the zoom level for the site. As each page loads, it checks to see if
  there is a stored zoom level and sets it again for the current
  viewing. If you change the zoom level of a site, any other tabs or
  windows that are open to that site will also change their zoom level.