hi mate
its good to see a person in the early stages of bonsai willing to take a tree right back and rebuild! it is one step a lot of beginners try and step around this as they feel that taking so much of is either a waste or just dont have the heart so good for you mate
now, If I was to be growing this little tree, I would have given this one a little more time to thicken the trunk all good though. when we cut down like this what we are trying to create is taper and movement, in saying this if you want a more elegant tree taking the tree down while it is still somewhat thinner like this will create a more feminine tree as the taper will be subtle. if you want to build a more poweerful squat tree, thickening the lower trunk from the nebari to the first branch to the thickness required before cutting down to a useful branch to get the next section of trunk. once this is done the lower trunk will not thicken any more until the leader catches up and the transition smoothes in. when the new leader gets to about three quarters of the lower trunk, cutting the trunk to a new leader in the direction you want can be done.
now I take it with this little willow leaf you are wanting a smaller type tree? you should be able to grow a shohin sized trunk in a just a few years

(GO SHOHIN!

)
check out bonsai4me.com about building taper in deciduous trees. it is a very good article, easy to understand and overall a very handy site, you could read on that site for hours, the progression shots of the tree are great aswell
nice work mate

keep it up!