One idea reveals another

Having discussed my new ideas (with myself), and not having written further than the prologue and first two chapters, I then found another idea lurking inside my head. It's a good one, and also an old one i.e. it's been used before and is probably necessary, in that it provides an authentic link between what I'm doing and what has been reported in alien sighting history as fact. I'm writing science-fantasy, but there is factual content contained in what I'm attempting to do.
It's been fun, and also frighteningly difficult, tying up all of the different loose ends. Each of those first three chapters contains links to the other two, and establishes a beginning and a firm base upon which the rest of the story can grow. It's taken such a long time to get to this point, and I almost ruined it after reading something else. Now that I'm back on the right road again, I'm detemined that nothing will go so wrong again. Noel the Ultimate Proofreader has suggested that maybe now is the time when I should be approaching agents. Agents do, after all, prefer to be involved in their clients' projects, and this would be a help, not a hindrance.
Noel is usually right - I actually can't remember him being wrong! I'm not averse to this, but I'm really not sure which way to go: the writing is in its early stages, although the planning and thinking is not. I do feel that maybe I need to wait until I'm a bit further down the road, where I can prove that the story is one worth taking on, and that I can actually write it.
Noel has also asked me if I believe it should be written alone. It's a big project, and I'm expecting to write at least another book after this one. You might think that that was a strange question to ask of me, but as I've said before, Noel is no ordinary proofreader and he doesn't spare a thing. He asks what has to be asked. I've given other writers a hard time when critiquing their work, so why should I be treated any different.
I said to Noel that you could ask a million writers to write it, and maybe only five would write it properly. And each of those five would write it in exactly the same way, so it would be difficult to find someone who could help. Difficult, though not impossible. You have to remain openminded in everything, or you will eventually get it wrong.
All sounds a bit precious, doesn't it? Ha - 'My preciousssss!' I'm wearing this new story around my neck like a ring on a chain - only I'm not about to take it to the Crack Of Doom to destroy it. And if an agent likes it, and offers to take it on, would I howl and say 'He wantssss it, my preciousssss!'
Jeez, I'm cracking up...