Hello @lednevandrey,
Welcome to the Maxon developers forum and its community, it is great to have you with us!
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About your First Question
The issue with your script is that you never insert your bitmap shaders. A shader must be inserted into a scene graph just like any other node before it can be used. Referencing a shader in a shader parameter does not replace inserting a shader. While for shaders this might be a bit surprising for beginners, one can look at it from an generator object angle to gain clarity. You would not expect to be able to link a that cube object into the document first. From this angle it is a bit more obvious that shaders are not any different and must be inserted before being linked anywhere.
In most cases shaders are owned by the material which use them and inserted with c4d.BaseList2D.InsertShader(). But there is some complexity to how shaders are structured when shaders own shaders. See Base Shader Manual: Access and Structure (C++) for details. The manual is for C++ but also applies to Python.
So, for the displacement part it should be for example something like this.
import c4d
import mxutils
# ...
path: str = storage.LoadDialog(type=c4d.FILESELECTTYPE_IMAGES, title="Select a texture for the Displacement channel")
if path:
# The mxutils.CheckType call is here so that we can be sure that allocation did not fail. Then
# we insert the shader into the document by attaching it to the material which itself
# is being inserted into the document.
shader: c4d.BaseShader = mxutils.CheckType(c4d.BaseShader(c4d.Xbitmap)
material.InsertShader(shader)
# Now we can link the file in the shader, and shader in the material. A shader can only
# be linked/used once by a material in the classic APU of Cinema 4D. So, if we wanted
# to use #path twice, we would have insert a second shader for the second usage.
shader[c4d.BITMAPSHADER_FILENAME] = path
material[c4d.MATERIAL_DISPLACEMENT_SHADER] = shader
Cheers,
Ferdinand