Not bad actually. Is it too complicated? It's still better to have more control than no control. I could perfectly live with it, you still managed to keep it minimal and to the point.
Will there be a way to add/delete layers like with Multi/Sub material so in case you need only 3 layers you don't have a huge list?
Does the mask checkbox grey out when layer is disabled?
Variable count is possible, but fairly complicated. I am not sure if Ondra would want to mess with it. As for freezing, it's a little more complicated than that.
- If there was no material in a layer, both spinners and checkboxes would be frozen
- If there was material but not a map, then map spinner and map checkbox would be frozen.
- If there was a material and a map, but material checkbox would be unchecked, both spinners and map checkbox would be frozen
- If there was a material and a map, but map checkbox would be unchecked, then map spinner would be frozen.