How to Implement open DWG, Custom Entity Processing, and Serialization in Autodesk Platform Services (APS)?

I am currently migrating from an ObjectARX-based AutoCAD application to Autodesk Platform Services (APS). My goal is to implement the following features using APS:

Allow users to upload DWG files.
Apply custom logic to extract and analyze drawing entities (e.g., area, dimensions) and compare these entities.
Serialize the processed data into JSON or XML format.
I am looking for guidance on how to achieve this with APS. Specifically:

Which APS APIs should I use for file upload and accessing entity data from DWG files?
How can I apply custom logic to extract and manipulate entity information (such as area and dimensions)?
What are the best practices for serializing the calculated data into JSON or XML?
Any advice or examples would be appreciated!