When it comes to the first book of a series, how much of the query should dwell on the overall Main plot-line of the series (that's only beginning in the first book) verses the specific ending-plot of book 1 alone? (being that it has both). This is a Fantasy series (could also be YA) with a set number of books that completes the main story. Course, from a newbie, is something like this a plus or minus when you receive it?In your query, address book one. At the end of your letter, state that you intend this book as the first in a series of x number of books, following the story of A as he/she does whatever. Don't go into much more detail than this. The publisher will ask about it if they're interested.
Now, if it's an epic adventure that really cannot be done in one book, you could add a second page to the query that gives a two to three sentence breakdown of each of the additional books.
In general, for a first time author, book one of the series should be written as a stand-alone novel. You can leave small clues in the book that can be pursued later and you can create an ending that allows for a sequel but you need to have the story complete in itself in case the publisher decides not to publish the rest of your series. Nothing is more disappointing to a reader then a book with a cliff hanger that never gets resolved.
Whether it's a plus or a minus depends on how well written the book is. If it's great, I'm going to be excited that there are more on the way. If it turns out the book sells well, then I'm going to want a new one each year until the series is done. If the book stinks, then it really doesn't matter.