On an average, space of how many economy class seats is taken up by a suite?
The size of the seat is slightly different in each airline, but according to this table, 32"×18" is the smallest, and most common, economy seat. That is 4 ft².

According to the article you linked, the largest suite is 125 ft². That is 31¼ times more.

Remember, however, that space is not the only consideration. The main consideration for aircraft is weight and obviously first class passenger does not weigh more than economy class one.

Now consider that those 853 passengers, with baggage, will weight around 80 t. Maximum take-off weight is 575 t of which 276 t is empty weight and the tanks can take about 260 t of fuel. But that leaves you only 39 t for payload with full tanks! So on very long routes, the aircraft can't pack 853 passengers anyway. The 500 is about maximum that makes sense (for long range variant, which is most common).

So they don't mind wasting some space for luxurious first class if they can charge premium for it.