Graphic Novel formatting?

When the co-author and I began writing we had one important question:

How do you format a manuscript for a graphic novel?

We had no clue. We knew that there would be panels. We knew that there would be pages. But we didn't know how to break all of that up into a functional manuscript that would tell us how many panels per page and thus, how many pages of the graphic novel we'd have.

The co-author had no former background in comic books, and me as the illustrator with no former experience in writing a graphic novel manuscript, we first approached it in an odd way. I figured, the least he could do is panel the dialog out with one or two characters talking, three at most. He also formatted the original manuscript in scrivener (not the best idea). We assumed that roughly a page of the manuscript would equal a page of a graphic novel, but we didn't know how the math worked out or why it worked out that way. 
In the end, we were given a sample page from our editor that looked something like this:






Each page is labeled with the page number at the top.
Each panel is labeled with the description at the top in bold.
Character names are all caps. Each dialog text has a number before the name so at the end you'll know how many dialog bubbles there should be.
Each page needs to be planned out as to how many panels you want for a particular page. You'll notice that Page 2 has only 6 panels and Page 3 has only 3 panels.
So you're going to have to figure out how many panels you want on each page. 
How do you do that? Well, I had to figure that out while going through the story with Keith. Initially, he only knew where he wanted to section off the panels, but he had no idea how many panels there should be per page.
So, during our edits, we reviewed the manuscript. I thumbnailed out what I thought each page should look like and he adjusted the manuscript to reflect that.
In the beginning, I was sketching out the art for each page, but then as we got further along, I stopped sketching and just started figuring out how big/small/long/tall the panels would be and what each page might look like. 

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It took us about a month of reformatting our script and thumbnailing out the panels. We started the editing session with roughly 280 pages of script. We ended the editing session with 282 graphic novel pages. 

Now we wait to hear back from the editor and see how much more we need to cut, thus rendering all my thumbnailing completely null and void. Ha!