Just one hank, not all. And take a look at the Gerr system.
In my experience the best way to rig a headsail downhaul is:
Use a very light line. 1/8" or 3/16" for a boat your size. You don't need more. Length is: length of your forestay plus the length from the forestay to the middle of your cockpit.
Tie one end of your downstay line to the head of your jib (use a bowline if you're going to be changing headsails; a buntline hitch if you just use the one jib)
Pass the line through one or (maximum) two hanks on the way down the forestay (there'll be too much friction if you do more: the forestay may jam)
Turn the line back through a block you've installed at the base of your forestay
Then run it back to your cockpit, where you'll want some means to cleat it off
Once you've purchased the line and the forestay-base block, you can experiment with different ways of rigging it. You don't have to stay with my suggestion. (Though I think you'll end up with it anyway!)
As an alternative: there is also something called a Gerr downhaul. This claims to:
1. Roll your jib into a ball on the foredeck when you drop it, thus eliminating "jib overboard"
2. Give you the alternative of dousing the jib, not dropping it: ie pulling it into the forestay so you lose power.
I've tried it and don't recommend it: too much friction in the system, so you have to pull like crazy for it to work. But, if you're interested, here's a link:
http://www.widgetsailor.com/myboat/downhaul/jline.html
The basic system I've described is a piece of cake. You'll love it.