Being that you are running a server installation from a central file source with your NAS the Database would be?/should be on the server, imo. When you setup your watched folder location from in Roon on any of the other installs it it should point the server directly to the NAS and the server will handle the database/processing.
SQ wise there might be a benefit on hooking up your dac to the laptop or PC versus the server as that is where the processing is going on, but that is just a guess on my end and certainly not fact, it may not even be feasible on your end depending on location of PCs/system.
See this post from @andybob about 2012 installations. He has a couple of helpful links as well as it looks like you may need to tweak a setting or two.