I think you should join a writing group. Even if it's an online one. The outside perception you get is INCREDIBLY valuable. They see things you can't. Be sure to take their criticism well. If after careful study, you disagree with their criticism, don't make the change, but be sure to consider it and not be offended.
Certain basics:
Huge novels like yours are hard to sell as a first novel. THis is NOT to say it can't be done. It has been done and will again, I'm sure. But publishers have to be really wowed to take a risk on a huge book (they cost more to publish and don't have much markup on the cover price, thus must make more sales to break even).
I think what EUOL (Brandon) did was the smartest approach. It is extremely rude to do simultaneous submissions (sending the same manuscript to more than one publisher), so his approach was to write first novels only. Novels that were self contained, but had the opportunity for sequels. THat way he would have several manuscripts to several publishers (it's not generally a good idea to send volume 2 of a series to a publisher) and if they wanted a trilogy, he could deliver. So my advice is to write a book unrelated to your current manuscript next.
Also, don't get disappointed easily. First manuscripts don't usually sell either. However, it will do you no harm (well, it'll cost you postage and printing) to send out your manuscript. So start passing it around while you write your next book.
You'll want an agent eventually. Some publishers won't even LOOK at a book that doesn't come from an agent (it provides a screening process they don't have to spend man hours on). However, even if you do get an offer from a manuscript you sent out yourself, then you want an agent before there's any agreement on amount. It's not hard at all to find an agent when a publisher has made an offer. All you have to do is ring up an agent's office and tell them X wants to publish my manuscript and I'd like Y to represent me as my agent. This is like free money to an agent. He already knows he's going to get something.
Which is the next point: NEVER PAY AN AGENT. Money should always go from the publisher to the agent, who takes his fair cut and gives it to you. I was told this by a publisher, an agent, and an attorney in the intellectual property business. It's sound. Good agents don't charge fees. They make more money the more they get for you, so you can trust them to fight hard.
Finally, start networking. Go to sff cons (this is a sf or fantasy, right?) in your area (game cons not so much) or any of the major ones across the country. Shake hands with the agents and publishers there, introduce yourself, get to know them. When your manuscript crosses their desk, that makes it much more likely they'll remember you and be more interested.
edit: oh, and keep in mind, I'm not published yet, at least not as a novelist. However, I got all of this advice from successful authors, agents, and publishers, so I think it's pretty reliable. I'm about at the same stage as you, reworking my draft of my first complete novel manuscript and writing a second.
