[Konon]

What's your take on the poster dimensions? I see you suggested 1000 x 1426 like Fanart.tv while TMDB use 2:3 aspect ratio on their posters.
Before I preferred the 1000 x 1426 dimensions because it made it easier to adapt DVD covers into posters. In fact I was in favor of it when fanart first started their poster section.

Now that DVDs and all in general physical media is being phased out I've come to prefer the 2:3 poster aspect ratio that is the standard of way more sites. Not only TMDB.
Most Kodi skins, including the default Estuary, also use the 2:3 aspect ratio so creating a new site with artwork for Kodi with posters that doesnt fit seems a bit dumb.

I was thinking 680x1000

I'm not interested in the highest quality artwork, as other sites have that covered. Interesting thoughts on the aspect ratio 

And why do not you want to use the size 1000x1500 - the KODI standard? On large TVs, the small sizes of posters look bad.