Considering that it is not a boxed but fluid layout it depends on what resolutions of your users you want to refer to.
In your place, I would make sure to favor the most popular resolution, 1080p.
And at that resolution 927x900 is the minimum size that allow the image to be sharp.
I would advise you to set in the global configurations, in the SEO section, search engine frienfly url and use url rewite both on.
To do that you will have to rename the htaccess.txt file to .htaccess (in any case it is clearly written where you will make the changes in the SEO section).
By doing this your URLs will not contain index.php which is not elegant and is not functional for SEO.
If instead the setting was that because you are still in the experimentation stage and you already know the things I wrote to you, sorry for the useless advice 🙂