Teach me how to read data from an ECU

I have a need to be able to read full data from Bosch ME17.8.5 ecu. While there are a number of packages available on the internet to do this, they are expensive and limited.
I have worked in the IT industry for 30+ years, and have a moderate background in basic coding, but i would like someone with automotive and programming skills to help me start building my own application that can do this.
I intend to use this knowledge to tune / duplicate my existing ECU's.