Found a great set of articles on how to modify a WordPress theme. What I didn’t find was a concise “table-of-contents” set of links to the entire series… So here it is:
Dissection of a WordPress theme: Part 1
Dissection of a WordPress theme: Part 2
Dissection of a WordPress theme: Part 3
Dissection of a WordPress theme: Part 4

Many thanks to John Godley & UrbanGiraffe