best location for media cache on large documentary project

So I'm wrangling a large documentary project for a client...  One of the first things I do when digging into how a client has set up a project, is to make sure there is sufficient empty space on their startup drive...  And try make sure that their workflow doesn't add data to the startup drive in the background because...  not everyone checks to make sure there is always sufficient space available on their startup drive...

So wondering in terms of performance, should the media cache be kept on the startup drive (which in this case is a SSD) or the very large hardware raid where all the media lives...

And where should the .cfa and .pek files live.  I've tried setting that up to save them next to the original media files "when possible" but this adds a lot of "extraneous" files to the media folder...  

Just my OCD kicking in trying to figure out the cleanest, neatest, most efficient workflow.

Thanks as always,

Michael