I have many ideas that can potentialy make a good novel to write.
Almost everything is ready in my mind : the charachters, the setting for the story, the beginning of what could be a plot (altough, I'm not too much in the classic idea of a plot)
But...
While in a short-story, the quickness of the story line development and the area of possibities for ending the story is large and various (for example, I frequently use sudden and steep ends) I find the mechanics of a novel more difficult !
It's a bigger machine, with a greater inertia force, so it's harder to stop all this stuff you placed on the rails... must I decelerate to manage a smooth finishing, or let it go crescendo, but a crescendo ending in what ? And will it sounds good ?
I feel that in some cases It could be something less convergent than in a short-tory ending, more open but, I still not find how to make it !
Simon P. Clark is right as always and as I've written through seven ending I'm probably the worst person to advise you, but it sounds as if you are used to short stories. The transition between the two is more difficult than most imagine. I once went to the prize-giving for a short story award and the woman was saying she was now writing a book but having some trouble with the extended format. That made me smile because I've been accused of trying to crowbar an entire novel into a short story. I think everyone is better at one or the other, even if they eventually become very practiced at both.
You're right about the subplots being hard to tie up at the same time as the main story line. Some of them should run at different speeds so tie some up well before the end and leave a couple of others to the fizzle after the explosion.
There are different ways of ending novels, of course, and it depends a lot on the genre (for example, children's fiction tends to require more of a wrapping up than adult). In general I think the idea of a denouement (conclusion / crescendo) just before the ending, which is followed by exposition and wrapping up, works best.
So, like an explosion, but then there's still some fizzle left (if that makes sense?)