sorry for the late reply. This guide from the Ouster blog may be exactly what you are looking for. It explains how you can leverage pre-existing algorithms, originally designed for 2D image analysis, and adapt them to process 3D lidar data. The guide provides a step-by-step demonstration of this process.
Ouster also released Gemini, its own perception platform. Considering that you wanted to build the platform from scratch (as you wrote in your second post), YOLOv5 might be an interesting alternative to Gemini.