It should probably be stressed that the "they'll ask you to write something else" business really only applies to the wacky business of tie-in writing. If you submitted an original novel to, say, Tor or Del Rey, they probably wouldn't say "We have enough cyberpunk novels, write an urban fantasy instead."
That's the sort of advice you expect to get from your agent instead.
As for the outline, it's a balancing act. You don't want to it to be too dry or mechanical, but you also don't want to bury the editor in details. I'll maybe throw in a line or two of dialogue, but save the rest for the longer version of the outline I'm saving on my computer, just in case I end up writing the book. When it comes to fleshing out any new characaters, though, that probably belongs in the sample chapters, not the outline. Usually, all you have a room for is a brief capsule description: "Dr. Edwards, an eccentric robot expert . . . ."
Hope this helps!
Sure does! Thanks a bunch!

If a story is turned down after you submit it, is that it for it, or can you try again after you've gotten other stuff published?
FWIW...Peter David, I recall, tried and failed over and over to get Pocket to accept his Q-meets-Lwaxana story concept (which, of course, became Q in Law). They only accepted it when he made an offer they couldn't refuse, concerning that Borg novel they wanted him to write (Vendetta): "OK, OK, I'll write the darn Borg book--IF you accept the Q/Lwaxana book, too!"
And of course, he got a good word from the late lamented Majel Barret Roddenberry--which was a plus, naturally.

(ADD/Asperger's moment: Irony of ironies: Vendetta actually got a disclamer stamped on it--something about there being no "former-female" Borg...?
Anyhow, the book they were begging him to write...ended up getting dissed by TPTB. *sigh*)