Will B4 main volume respond to midi expression data so that I could control the volume this way?
Are there any settings that must be done to do this?

tonkan, yes the NI B4 volume along with other messages including program change numbers can be sent from a controller keyboard to operate on the B4. The messages you can send are listed in the manual that comes with the B4. The B4 does a very good job of emulating the Hammond B3.

I hope this helps.