Image Styles
Hero banner: 1920 x 700px (1920 is really a minimum width for full screen images, anything less will scale up on the majority of monitor sizes and look poor)
Hero banner (thin): 1920 x 600px (or same as above for nodes hero banner field.)
Card overlay: 640 x 480px
Card: 480 x 480px
Node teaser images:
Minimum: 480 x 480px displays nicely inreferenced in Cards.
Recommended: 640 x 640px so a better crop can be made by image styles.