How to organize a shared cache for qsys systems?

_hw.tcl files, when created for new custom components via Component Editor, get placed in the Quartus project directory for some reason.  Back in the day, they used to get placed along with the location of the HDL code that defined the custom component, making it easier to have that connection between _hw.tcl and the code.  As for the connections between files, simply open the _hw.tcl file and you'll see the paths pointing to the associated code.  Remember that .ip files define an instance of a component with a particular selection of parameter settings added to the system so it should point to the _hw.tcl, I believe.

I can't help with the prior question.