I am in the process of creating a character that is "usable" from... most angles (-90 - 90) using "linked" switch layers for each body part. I'm working on the same sort of thing, learning as I go :) I'm finding using 3D rendered raster layers for this much easier going than dra...

If you are using Photoshop, you can go to Layer/Matting/Remove Black Matting (I don't have it open, so the wording may vary) This will get rid of that seam.