You can buy the vocal selections for about $23: https://www.amazon.com/dp/0571529976/
Everything that can be bought, should be bought. Encourage the artists you like. This sub is (or should ideally only be) for "rental only" items that cannot be legally bought.
For piano sheets, I go to musicnotes.com, they're usually about $5-6 per song. La La Land is dominating their top download chart right now:
http://www.musicnotes.com/topdownloads/
Or if you want to wait for the whole book, it appears to be available for pre-order on Amazon (will be released Jan. 26th)
https://www.amazon.com/Land-Music-Motion-Picture-Soundtrack/dp/1495088243/
I read the book years ago, so I may be misremembering. However, the fact that the Times article bizarrely misrepresented itself as breaking a story that was already known for decades made it suspect in my view.
Wilson's book is easily found....unless you are a Times writer.
https://www.amazon.com/But-He-Doesnt-Know-Territory/dp/0816667705
Just picked this up after seeing it recommended in the technical theatre subreddit (or maybe it was here…?): Mixing a Musical: Broadway... https://www.amazon.com/dp/0240817591?ref=ppx_pop_mob_ap_share
“The Music Man” is an interesting film because a lot of stage elements was worked in, especially the “Luda Rise/Dream of Now” song. That was a deliberate choice by the director, let’s have spotlights and different groupings as we had on the stage. (If you ever get a chance, read “But He Doesn’t Know the Territory!” all about the creation of TMM by Meredith Willson.
If you want some information on music specifically. there's a book called Sondheim on Music which is a written out interview with Sondheim.
Here's the amazon link but you could probably get it at a library: https://www.amazon.com/Sondheim-Music-Minor-Details-Decisions/dp/0810874369
You've got the right idea.
Learn DCA/VCA first, that will be biggest improvement.
Then get into scenes after you understand that. Don't do too much in scenes at first, just mutes and VCA assignment.
And read this: https://smile.amazon.com/Mixing-Musical-Broadway-Theatrical-Techniques/dp/0240817591
Check out Neo-Riemannian Theory if you haven't already. A "slide transformation" is a progression between two chords that share a third (eg. C and C#m). Your chart is basically an extension of that concept, adding the 7th. NRT works strictly with triads, I believe. Maybe you are on to something. "Parsimonious Neighbor Chord" seems like an appropriate name!
You may also want to check out Hollywood Harmony: Musical Wonder and the Sound of Cinema by Frank Lehman. It focuses on harmony in film music, using what he calls Pantriadic Chromaticism which is basically tonal harmony used in non-functional ways resulting in chord progressions similar to yours.
Berlioz/Strauss' Treatise on Instrumentation is another good one.
It's not completely updated through the past 6 years, but I really like Broadway: The American Musical, by Michael Kantor and Laurence Maslon. There's even an accompanying documentary with footage from a bunch of Broadway shows. (The documentary, however, is over a decade out of date. Still worth a watch, though, especially since it's hosted by the one-and-only Julie Andrews.)