How to: High poly to low poly normal map + high poly texture + normal map of texture detail This is hard because I dont think there is a "correct" answer to this.
Basically I want to use a normal map of a high poly model on a low poly version of that same model. This I learned so far. But I can't find instructions on the following:

I would like to paint a texture for the high poly and use this texture on the low poly too. 
On top of that I'd like to use normal texturing for the high poly texture e.g. giving it the small detail shading.

To sum it up:

High poly with (color and) normal texture
-> 
Low poly with the normal map of the high poly model + the color and normal texture of the high poly.

How many and which maps do I have to bake then and how many textures does one need for the low poly version?
Is the texture applied to the low poly version or its normal map?

To visualize this let's say we have a modeled brick wall. 
We paint a color texture for the model, the texture has little cracks and sprinkles so we use normal when I assign it to the material of the model so that these small details are shaded.

Now that whole thing shall be put onto a simple plane (or a low res model).
Not just the normal map for the model but also the color texture plus the normal shading for the color texture. 

I know this is like normalception and kind of confusing but I didnt know how to put it in words better with my noob knowledge.

Meanwhile I will trial and error my best, cheers!
You said you know how to bake a normal map from hi-poly to low-poly. It's the same for color texture.
If you use blender internal, bake textures instead of normals in the menu.
In cycles, you can choose 1 of the 3 diffuse maps (color, direct, indirect). The diffuse color should be what you need but if you want to combine the 3, you have to add direct to indirect and multiply the result with color.

About normal map : painting a normal map is a bad idea. Some softwares allow you to do it but if you want to paint details, use a bump map (B&amp;W). I'm not sure about that but I think the normal baking adds the bump map inside the resulting normal map (blender internal). Else you'd better paint it on the low-poly mesh.