That’s a great plan! I’m straining to save mine to expand mine.
Discussion
Modular is a very deep rabbit hole. For myself, I'd build something small and compact. "Low cost" and simple.
This is the new box I started to build. To be honest the case has a lot of space going spare and I’m taking it slow filling it up. 
Predictive text, arrgghhh that’s meant to say “planning to stack mine” not straining etc.