Your idea of making each card out of parts seems like a very good one. With the four suit symbols, the characters 0-9, A, J, Q, K, code to draw a rounded rectangle border you can draw most of the cards. The benefit is the amount of texture data needed is very small. You could make the symbols and characters quite big and they would still fit in a small texture. Making them big lets you scale them to whatever size you need for that device. Then add art for the picture cards and you can draw all 52.
As for how to actually draw them there are two ways. You could make a texture for each one, assembling it on the fly in a RenderTexture
. This is cheap to draw but needs memory for the textures. How much depends on how many cards are visible at once.
Or you can draw each card from its parts on-screen. This means you are drawing more things which can add up, but does not need any additional texture memory as you are just re-using the textures for the symbols, characters etc. over and over again.