I might put my three images on foamboard in a strip. I like having the two darker images on the outside of the lighter one as it creates a contrast and looks good presented together.

For these A4 images I might put them on white foam board, then back that onto black card to bring out the colour and add to the darkness.

As its A3 I will either do the same for this image by mounting it onto white, then black board, or I will window mount it.