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!
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.