If you don't want to write a novella--you're committed to a novel--you have to crank out AT LEAST 30,000 words for middle-grade or YA readers, 50,000 for adults.
At the same time, you don't want to be "bore-geous," what Ayelet Waldeman calls writing that is long, lush and vivid but does nothing to further the story line. Neither do you want to add subplot upon subplot upon unnecessary scene upon unnecessary character just to make deadlines, fill up a word count, pad the pocketbook, or all of the above. (The latter often happens with books that start as serials, like those of Charles Dickens, to point out an example that will hurt no one's feelings and probably not constitute lashon hara.)
The problem is that I HAVE A LIFE, and not a very convenient one at the moment. I have more immediately remunerative work to complete, a husband and children to feed (bli ayin hara!). Tushies to wipe! Candyland to play! I am haunted by the desire to fill in the story of these characters, but have been cruelly separated from my PC.
Even when I resort to writing in a notebook while supervising my children's play, self-doubt leaves me thinking, "Can I think of enough details and plot twists to fill a novel? And what if I'm just plumping this goose up so it's ready for the rejection-letter-shaped ax!"
Sometimes, I finally sit down at that PC and can't even figure out where to start. To prompt me a bit, I'm now improvising a bit on the Snowflake Method, invented by Randy Ingermanson. I'm going over every hinted-at back story, every interesting character, every "off-page" alluded-to event that appears in the initial short story and trying to extend, extend, extend. I am now at just under 7,000 words...and I can't imagine how this baby is ever going to get done!
I know I'm not alone on this. A quick Google search about novel-writing included an article subtitled "The quiet h*** of 10 years of novel writing," by Susanna Daniel, and a blog entitled "The Long Path to a Novel" by Rachel Connor.
Check back with me in two months to see if I'm any closer to the "Great American Jewish Sci-Fi Novel's" completion.