Digital BW, The Print

Hello,

I've decided to load our Stylus Pro 7500 with Piezo K6 and buy it in  
bottles.
However, when looking at the Inkjet Mall site I'm getting a bit  
confused.
I can't find any information which shade to exlude from the K7 inks.
K2, K4 or K7 any suggestions?

Do we need to flush the printer after only have used MIS UT 1 inks?
Any guess when the sepia ink comes in bottles?

Thanks,

Hans