Approaching extended chords in songwriting

Hey there :wink:
I have a question concerning music theory and songwriting. Since there seem to be many professionals on this forum I wanted to approach you guys.
Basically I’m relatively confident with all the content that is provided on Hooktheory and in “Hooktheory I”.
The question that is now bugging my mind is how to incorporate extended chords into my songwriting progress? Do for example 9th chords have different scale degrees than 7th chords or can they just be used as simple extensions for existing chords? I’m very interested in R&B and Neo-Soul production but I can’t find any serious literature about it. I want to learn all about rhythmic styles, voicings and patterns used in these genres.
Do they borrow their basic concepts from pop-music or should I put my focus on Jazz Theory? Or just start analyzing songs that i like?

I feel like I’m overcomplicating the whole songwriting process.

Thanks in regard!