I'm working with a new writer who is quite good at what she does. One of her big questions is that she wants to know if she's managed a good balance between all of the threads in book 1 (she's planning a trilogy) and if there is resolution. This is a common question I get, especially when writers have already plotted books 1 through 5.
First off, I firmly believe as writers that we shouldn't think so far into the future that we've already figured out that Uncle Abe will have a prominent role in book 4 after Cara his second wife has her story showcased in book 2. Let's focus on the material in front of us: book 1. Don't get ahead of yourself because writing a book is a daunting experience and requires a lot of love and time and devotion and a commitment to realizing what's working and what isn't. One book at a time.
For the most part, people who have dreamed up these sagas and trilogies are doing so because the commercial viability of more than one book is strong, and has been proven time and time again with such writers as Rowling, Tolkien, Jordan, Adams and so on. These writers pulled it off because they truly had a wealth of characters and story to share, so much so that it wasn't enough to fit in one neat, tight, compact volume. That's not the norm. Sorry to break it to you.
So, you have big ideas and what you think are many of them. Fine, good. But do me and everyone else a favour: please be sure to tell us who that odd man/lady/dog/ghost was before ending book 1. You cannot simply foreshadow with a new character, have them pop in occasionally, and then not let the reader know what the point of all of this secrecy/suspicion/intrigue/mind game was. Do you know what answer I inevitably get when I ask writers about said mystery character: I'm saving that for book 2.
NO! You are not and cannot save that for book 2. Do you want to know why? Because I'll be too pissed off at you, dear author, to bother reading book 2, that's why. Readers hate trickery, they love closure. So please close off all loose ends and make sure your book 1 is complete in and of itself. It should be able to stand alone and apart from the others. Don't make readers have to read/buy another book. Never a good tactic.
My suggestion to all you trilogy writers out there is to write your book, with as many of the ideas as you have set out, and just write. Forget length, just tell the story. I suspect that 8 times out of 10 one volume will suffice. By the time you edit and tweak and tighten, that 1000 page tome will be a succinct, fast-paced 500 pages that tells a multi-level, rich, detailed story without the need to drag it on over many volumes that are weak, scattered, and grasping at life.