I noticed that exported models will have a different material for different textures and colours. Would it be possible to bake it all into a single texture and use a single material?

Yes, it's been requested many times already and I feel like it's an important feature to have. Currently I'm experimenting with a way to get this working!

My apologies. I did have a little search for this topic but clearly not thoroughly enough.

Awesome work. Much appreciated.

Using the same material for the faces that use the same texture would be an excellent starting point. Having 4+ materials with the same texture seems to eat up a lot of frames on mobile (That is my current guess), and I don't know if it's worth trying to de-duplicate them by hand.