Trilogy Question

You can still query it when it's done, just be aware of the obstacles with a non-stand alone series, and know that the odds are against you. But if the book is great and all three are finished, there's always a chance someone will love it and your voice. If you have other work, you can query those and later tell your agent about this great trilogy you have. It's just far easier to break in with a stand alone book.

However...

Even if the first book doesn't stand on its own, there still needs to be a sense of resolution to satisfy the reader. The full story may not be complete, but one step of it is. If the book is all build up and doesn't end in some way, I don't think you'd have any success with it because it's not a complete book, if that makes sense.

I'm reminded of Kathleen Duey's "Skin Hunger." That book is the first part, and it's not a stand alone, but it does end with the protag reaching an important step of the story. There's a sense of resolution, even though you know it's just the beginning.

Seconding Danthia's post.

And even in series, each book needs needs needs a resolution of some sort (that's me as a reader talking ) . I get really annoyed if I need to read 10 books to get to the resolution. Your main plot would obviously go on but some sort of resolution and climax is, IMO, essential.

Hard to say from that since I don't know what the goal of the novel is You'll have story question poised at the start of the novel. Protag must do X to achieve Y. Even if the protag hasn't gotten to X yet, there are lots of steps that need to happen before she gets there. Some of them will be major steps. If the first book ends with the resolution of a major step, and that major step was the driving force of the novel, then you're good.

Overly simplistic example:

If the trilogy goal is to rob a bank, then maybe the first book is all about them getting the plans for the bank. It'll be hard to do this, there will be obstacles, but by the end, they have taken the first step and achieved the goal.

Make sense?

All the MG series that I know of have at least a mini-quest or sub-quest for the characters to complete in Book 1. Something so the reader can sigh with relief. Like: if you don't find your plucky sidekicks for princess rescuing detail by the end of the month, you'll be screwed. Then our MC scrabbles around trying to find them against all odds. Whew, mission accomplished.

The first HP book is a great example of this, or the Golden Compass.

Do the boys have to overcome great obstacles to come together as a team? Because if it's just assembling the team, you might not have a solid enough resolution. Gathering the team is a common Act One event, but not a climax in and of itself. But if getting together is a major deal and there are conflicts and obstacles against this, then you'd probably be good.