Greetings fellow users,
Having found no answer to the issue that I am facing in the existing topics of the forum, I decided to call for your help directly. So here it goes:
I am working on a book layout trying to apply classical rhythm and proportions. The format is 140mm x 210mm (396,85pt x 595,26 pt), which equals a proportion ratio of 2:3, and the margins are set according to the golden ratio as described famously by Jan Tschichold. The size of my text frame, which is positioned according to the aforementionned margins, is 264,566 pt x 396,85 pt.
The issue that I am facing pertains to the vertical space of the text frame. I want to
#1. Have all the the lines of the pages align throughout the whole book
#2. Have (in addition to #1) the same number of lines on pages throughout the whole book
#3. Maintain #1 and #2 while being able to have, in addition to my main body text, different variations of text sizes and leadings for headings, subheads, block quotations, footnotes, poetry, etc.
Now to achieve this, I understand that I have to define a baseline grid which is in sync with the leading of my text. I have no problem achieving this. What I am having a hard time achieving is #1 and #2 when I add text variations with sizes and leadings different from the main text (ex. block quotation, poetry verses, etc.).
I am aware of the basic principle that to achieve this overall balance one has to define a vertical scale, which means that each departure from the main text should be an even multiple of the basic leading. But applying it in InDesign is a mystery for me.
I am able to add block quotations and other variations to the main text but forced to keep the same leading of the main text and baseline grid. I defined a baseline grid with an increment of 6 pt which is a multiple of the basic leading (12pt) and inserted my quote and poetry verses with a half-space (6pt) before and after. But now I want to be able to change the size and leading of these text variations while keeping the lines of the spread aligned. Here is a capture of my spread:

What increments should I put in my baseline grid in order to add any variation of text I want? How do I calculate it? Do I have to set the leading of my main text according to the size of my text frame?
I would be most grateful if you could enlighten me on that issue. I tried every possible increments for the baseline grid with no success.