Reddit is down to running with only one developer (and surviving fine).
How many people does it take to run/develop for Quora and why?
Isn't Quora "simply" a feature-rich forum system like Stackoverflow (with a different layout) ?
ps. why are we not allowed to see when a question was asked on Quora?
You can actually seem when a question was asked on Quora, if you click on the last activity timestamp on the question. It's just not that easily accessible because we want to emphasize the fact that each Quora question page is something that will last over time and not be transient. The page should mean the same when the question was first asked and when others visit any amount of time later.
I would say that given their ambition, it'd be a big mistake to ever look at its current state, as if it were a finished product, and then ask exactly what it would take to make/maintain that visible feature-set. That's leaving out everything that led to that point – which is not a clone of any other site – and all the options they've created for next steps, and all the hidden expertise/systems for keeping it vital.
You can get a superficial clone of lots of sites by treating their current instantiation as a frozen spec, and bidding it out. But you can't discover new constellations of winning features, and adapt the site endlessly to new problems and opportunities, without staff that knows and likes the codebase as if it were an appendage of their own bodies.
P.S.: Regarding your PS, click the timestamp representing 'Latest Activity' on the bottom of the right column; you'll see a dated log of all question-activity, back to when the question was initially asked.