1. should I explicitly set a height on images 2. should the explicitly set height be in px or rem and why 3. is there a better way altogether to achieve same height cards across a grid.

The aspect-ratio CSS property allows you to define the desired width-to-height ratio of an element's box. This means that even if the parent container or viewport size changes, the browser will adjust the element's dimensions to maintain the specified width-to-height ratio. The specified aspect ratio is used in the calculation of auto sizes and some other layout functions.