It's not so much the number of hubs but the quality and the 'market' you're aiming at.
You can for example write a shorter hub on a current 'hot' topic, or one which you'll know will be popular. Let's say the Soccer World Cup in Brazil 2014. You could write pieces for that nearer the time knowing that,once the event has ended, interest in your hubs will too!!
You can earn some money this way in a short burst of activity. Be prepared for a sudden drop off once the excitement is over!
Write medium term hubs. These will be slightly longer than previous and on different topics that you are confident enough to handle. You may get regular traffic to these but only dribs and drabs.
Evergreen hubs will bring in traffic long term - at least that's the theory! It doesn't always work out like that but if you create 'sustainable' hubs they should bring in cash going forward. Quality is the key.