Today I was remembering reading your thread, and I wondered if something I recently saw would be helpful for you. I know it clarified the importance of a scant 1/4" seam for me.
https://www.diaryofaquilter.com/2011...t-14-inch.html
Additionally, Amazon (there are also other sources) sells something called a Perfect Piecing Seam Guide. You put your needle in the hole, and then use a piece of painter's tape to create a scant 1/4" seam guide on your machine. And, of course, you can create a ridge to follow by applying a couple of layers of painter's tape.
I love what you are making. It is beautiful!