If you want it to be smooth and not astringent, I would stick with the carafa and not use the black malt. However, 1lb of carafa and chocolate is a fair amount of roast malt. You may want to consider cutting both back to 6oz or 4oz?
Also, there is negligible difference between special B and C120L. Maybe switch one to a mid-level crystal like 40L, 60L, or 80L for a little more complexity? Cut back the total crystal used to about 1lb.