How to optimize the use of multiple materials in one object?

Hello, I’m new in the world of game development, so in unity.
Currently, I have all the objects I’m going to use in my scene but the problem is I don’t really know how to deal with textures and materials.

For example, I’ve got a door that’s made of wood and metal, so i mapped the wooden part and the metal part, created two different object and assign it to the object, but i read this wasn’t optimal at all.

Also, I’ve read about uv baking but i didn’t get it clearly, would you tell me how should i deal with materials in such cases?

hi;
its nice that u pay attention to these things at your start;
uv baking is a job for 3d model softwares like blender and 3ds max;
so its not about unity in uv baking u create a texture that holds all the materials for an object like a car or a plane but its not about unity;

inside unity there are some plugins that can mix the textures and material togethers so u dont have to be worry about it any more ;

Thanks @Cuttlas-U for taking time to answer my question.
Yes, I know the textures are managed outside unity, actually I’m using Cinema 4D.
What would be the best method for unity to arrange the textures?

I mean is preferable, for example, to bake the uvs or directly make some scripting and let unity handle it?