I have been working on worldbuilding, plotting out, and writing characters for a science-fantasy series for over 4 years now, and I feel the time has come to take another stab at writing the actual thing after my first draft. The problem is I have expanded the world, plot, and character cast so much since that first draft that I had brought the planned book count over twenty! As there is no way I am realistically writing that many books, I decided to combine as many books as possible, and the number I was left with after fully compressing the planned book count for my series was seven.
However, although I am reducing the book count, I still want to keep my original plans as intact as possible by simply lengthening the 7 books to compensate. I have no problem with just the idea of having to write longer books, but the issue I have come here about is about the narrative structure.
Since my Book 1 is an amalgamation of the plans for my previous first four books, my plans for it don't really follow the thee-act structure, as each of these four books was conceived to be able to follow the three act structure and stand on its own, especially the first of the four.
NOTE: My books will be narrated as journal entries, written by the main protagonist and supporting protagonists. To avoid POV confusion, each journal entry is its own chapter, with the character authoring it clearly named in the chapter title (I got this idea from Rick Riordan's Heroes of Olympus Series). The main protagonist and supporting protagonists get the vast majority of these chapters, but every now and again, a side protagonist or even an antagonist will get a chapter.
How would I go about making my first book more of a single, coherent novel instead of reading like four different books joined at the seams?