So it's taken longer than first thought but it has been worth it. We ended up with 10 different textures for the style of the dials, but we have made them in such a way that each of the overlays work hand in hand with the backgrounds. This means that we have 100 (10 * 10) types of dials you can use in the game.
To make it even more flexible, I've added a mask texture alongside each background, which will allow me to change the colour in certain areas of the background, and thus create more variation on the backgrounds for each texture that I have. So with this in mind, I now have about 5 different "colour" schemes for each dial texture. so I make it 500 (5 * 10 * 10) different variations of dials that can be used.
Also there are currently 5 different layouts for the dials, I'll probably make a few more down the line but for now this will do. so that makes 2500 different combinations of dial setups (5 * 5 * 10 * 10)
Below is a video showing a subset of all these.