To make it perfect we will make a sharp highlight travel along the highlights.
Go back to illustrator. Duplicate the n_fillin-layer. Duplicate the layer´s shape and move the duplicate a bit to the left (pic 19).
subtract the top shape using the pathfinder. Use the scisors tool to cut the new shape at the top and bottom (pic 20). Delete the left parts, you should now have the perfect highlight-motionpath (pic 21).
In after effects create a new solid layer, about 20x20 pixels. Create a round, blurred mask. Copy and paste one of the highlight-paths from illustrator to the solid-layers position like you did in step 3. Move the motion path to where it should be (pic 22). Move the layers timebar to the right, so that the highlight doesnt start too early. Do the same for the second sharp highlight on the right side of the letter.

Voila, that´s it. Now repeat all steps for the remaining letters. At first it might seem to be a lot of work, but only because following a tutorial means a lot of reading, figuring out how things were meant and all that. Once you understood it and got some routine it will be easy. You can also save some time by duplicating the existing compositions and replacing the footage, renaming stuff and copy-pasting the new motion-paths into the duplicated comps.
As i mentioned at the beginning of the tutorial, the letters will start disappearing after a certain time (as you can see at the end of my example-movie). How long it takes before they disappear depends on the number of echoes, therefore it is important to have the same amount in the echo-settings for the fill-in and the outline layers. If you want to prevent the letters from disappearing then enable time-remapping on the letters final composition (for example on the "n_final"-comp) and make it stop at a certain point. But i think it looks pretty cool how the letters disappear.

Good luck.

Here is what the final thing should look like