As for subplots, I find that sometimes I start adding in so many of them that it gets to the point where I have to ask myself "how much is too much?" At this point it is literally impossible for me to, in a decent enough fashion, end WISB in one novel. I could end it, but it would mean the novel itself would be of a caliber I wouldn't be proud of and I don't think my readers, as few as they are, would be all that interested in a terribly shortwinded attempt to tie up all the loose ends. As such, we'll just have to carry those over into a second book and see what happens from there.
Do any of you find the same problem with your subplots? I have quite a few going in WISB. Thus far the main plot is James trying to save Laura and get home. There are just too many subplots to name, and most of them are in the form of questions as I haven't fleshed out enough of the ideas to adequately give an idea of the direction they are going.