The last time I used Wonderboard, the joints were really funky. They had kind of a mound at every long joint in the CBU. Really pissed me off and had me working way harder than I needed to. Not to mention it seems to be as stiff as a limp noodle. I haven't used it since.
I do like the spacings you used on those screws though. Looks like some nice precise work.
As far as the knee walls go, what are you using for the capping? If its a solid sill of some sort I usually slope it down about 3/16ths. When they come in to install the glass, they use saddle brackets that screw down into the sill and mount the glass to those. It allows for enough play for you to get a good slope and for them to get a nice straight install.