My recommendation might be a little different, so hear me out. I hate using CC7 because it's universal. You might want to use it for volume NOW, but you might want to use it for Wah or timbre or something else on some other patch down the line. If you set it to CC7, it's going to control master volume, on EVERYTHING...FOREVER. I would, instead, recommend setting it to CC4 (Foot Control) which is a completely MIDI standardized designation, but is never pre-assigned to any function in any synth I've ever used. Then set your individual patch to have CC4 control volume.
And there's an additional reason to do this with an organ VI. If it's a Hammond or electric organ: the volume rocker on a real Hammond is pre-amplifier, so if you have the amp drive turned up, the the tone will change as you move the volume rocker. Typically organ VIs will have a pre-amp volume controller built into them, so just use the 'Learn" command or similar feature to set it to CC4. Oh, also Hammond volume rockers don't take the volume to 0 either, so if you're looking for realistic control, you'll want to set it up like that.
