Small update: The ethernet driver worked, thanks a lot! The MAC defaulted to 00:00:00:00:00:00 though, so I had to set it manually. 
   
 I don't know why, but sleep also works now. Maybe it's because of something I did while getting rid of the App Store "Unknown Error". 
   
 Does audio work? - YES 
 Does HDMI work? - YES 
 Does HDMI Audio work? - YES 
 Sleep works, that's confirm - YES 
 Does it sleep and wake when closing and opening lid? - Closing: YES*, opening: NO 
 Screen brightness is controlled by Fn+Pause and Fn+F3 or Fn+up  and down button - YES 
 Audio control is by the right side - YES 
 Keyboard backlit is controlled by Fn+right arrow - YES, it's a hardware feature though 
 Screen snapshot is by Fn+PrintScrn - YES 
 Fn+F1 for sleep - YES* 
 tab power button to wake - YES 
 wireless card - NO, BCM94322 already ordered 
 ethernet - YES 
   
 * only after putting it to sleep manually for the first time 
   
 The very last minor thing that's missing is multitouch (at least two-finger scroll) on the Alps DualPoint touchpad. Is it supported at all? All in all, looks like the E5420 is a great base for a Hackintosh.