Finished! (Took me 3 days)
Private use characters are encoded in Variation Selectors and Latin Ext. D.
I've been wanting to do this kind of font for ages, think of it as a soft square or a hard circle. Since it's been so long, I can't really remember the exact source of inspiration, but I do remember it had something to do with kix and his work.
The ability to kern now has obviously made the spacing better than it would have been otherwise. Thanks, Rob.