I think I see the direction that you are trying to go in, so now that you have those class variables defined, you can access them within another pre/post build step.
If you had to create another pre build step python called import_asset/model you can do something like:
# -- grapping the asset path from previous pre step
file_path = self.custom_step("paths").asset_path
# -- do the import
cmds.file(file_path, i=True, type="mayaAscii")
In Maya, when you have your custom steps tab open, you can select the “paths” file that you have and click
run sel. If you have a print statement or some form of output to confirm that the results are what you are expecting, then this helps with the process too.
Hope that helps man!