Two notes from reading the first several paragraphs:

1. It seems one needs to know some Scheme in order to write these files:

https://www.scheme.org/

I don't think it's possible to just "wing it" by copy-and-paste.

2. I did not understand the introductory paragraph about how services "extend" each other. Does every service have hooks for possible extensions? What if a new service doesn't fit existing extension hooks?

(I can understand service dependencies of course, but it seems to go beyond that.)