I think they were only struck on the one side.
I could be wrong...
No, they were struck on both sides. The coin blank was heated and placed on an anvil which had one image, then struck with a punch which had the other image. I forget which, the anvil or the punch had the ‘heads’ image.
The dies were fairly small, which means the die-makers had to have pretty good skills (and eyesight) to carve the sometimes very intricate designs. There is some speculation that they used water-filled glass globes as magnification tools.