I haven't built this project (though I do have the PCBs somewhere in my stash here), so while I can't say for sure, I would assume CHA denotes the chassis connection. You'd run a nice chunky wire from that terminal to the same place near the power inlet where you have made your connection between chassis and IEC ground. Though I don't know the grounding scheme of this project, I'd reckon that's the path through which all grounds from the circuit (power ground and audio ground) return. I imagine if you check continuity between 0v and CHA, you will find the are connected. Again, I think this is all likely the case, but it will be important to double check the schematic and build documents.
Yes, 0v is the return path for your DC, which is then grounded to the chassis/IEC ground connection, assuming my guess above is correct.