Is there any sort of standard for human height in Blender units, or is it completely up to me? 9-10 units tall seems to be … too much.
Blender units are up to you. You decide what they are, then remember your decision. A blender unit can be an inch, a centimeter, a millimeter, a yard, a mile, a cubit, a furlong, whatever you want.
For making a human, I’d suggest either centimeters or inches, unless the human is going to be put in a scene with furniture or buildings, in that case I’d use feet, meters or yards.
Another thing you might try is using “heads” as the unit, since many drawing tutorials and references on artistic anatomy give various dimensions in “heads” ie: the height of a human head (adults heads are roughly the same size regardless of the person’s height). People range from around 6 heads tall to around 8 heads tall.
 and remember, when you’re done, you can always scale the mesh larger or smaller. [/edit]
I haven’t tried people yet, but so far I like to edit people-scale stuff on a decimeter scale; 1 blender unit being 10 cm. It seems to give enough resolution for detail (since a cm is .1 and a mm is .01 and we can easilt work with .001 if we have to …) while providing enough ‘space’ for most scenes that you would want (a 500 meter cube of clip distance? probably would want to keep thing within maybe 300 meters but you could eaily do most small sets in that I would think.
And I use metric, even though I don’t get it that intuitively, because factor ten scaling is simple and easy to reverse …