I was speaking with David from Veracity racing data he helped me understand some concepts that have worked well for him in working with DC and DM.
Essentially, DC is all about getting the custom dash designed - including switches/menu's etc. And DM is all about making it all "work". Counters, timers and logic should be done in DM.
I'm still getting the hang of it, but this has massively helped me grasp how to think about things and build out my files.