Dear Hans:
it's a stepwise process
- first set up a basic page style (next time in a big bookshop i'll take a look at the series) and set up a font; that way you get an idea how well things will fit
- then develop the structure + associated style mapping while writing (or converting)
ask yourself:
- do i need to render this differently - do i get the feeling that i enter too much code
if so, then add structure
This is how context itself evolved (after all, it was written in an educational context where structure, reuse etc is important). Just don't try to make up the style at the beginning, polishing it every now and then is a nice distraction.
Also, using metapost for the graphics is fun in itself (and may save you lots of time).
Thanks for the very thoughtful advice! Best wishes, Tom