Hi Neo, many thanks for info.
As user with many years experience I recommend to work with a stable and vary adaptable page builder with high customable options (diff. colors for different elements e.g. H, backgrounds, etc.) as well as colors for layout elements.
In this case you will have one master "template" and your monthly templates will be much easier to create. Additionall the installation of demos should be highly automated ... like e.g. pop-up window at installation of template and system asks you "would like to install template-demo XY?".
This would be great.
But if this takes long, then I seriously have to think to switch to WP (I tried in the past but I was not really satified from side of development; perhaps with your WP-template Creatus it's much easier.