You are on the right path. Look into the below section in the CAS developer Guide for further details.
Part 3::Loading data into an MDEX Engine
• Creating a Forge pipeline to read from or write to a Record Store
For tagging properties/dimensions you will have to follow the usual steps to map the source values to properties/dimensions.
Once content is inside Endeca, that is what I understand from your first post, you can use the OOTB cartridges (like results list, record spot light) to get the content and display it (customize your jsp to make them look as you want.)
If you don't bring data into Endeca, then you will have to write a custom cartridge handler to pull data from a discussion forum at run time.
Let us know what approach you are taking.