The tone stack is called Baxandall style. It is a classic design from the RCA design handbook. The advantages are: low phase distortion and low interaction between controls; it is used in most Hi Fi applications I have seen. The tone stack calculator is here:
http://www.duncanamps.com/tsc/index.html
The sleeve is always direct to ground AFAIK.
The balanced out is as complicated as it is because the high gain of the pentode was necessary to go with the rest of the microphone schematics this output is a part of. This high gain is good because it allows the preamp to work well with a large variety of equipment including multi-track tape machines. In the final design I have a pot before the output stage.
In order for the balanced line to do its job properly, the secondary impedance of the transformer must be more or less matched to downstream inputs. This impedance is often 600 ohms so the output impedance of the transformer should be as close to this as possible. Mismatched impedances will affect frequency response adversely.
I took this preamp to a recording studio recently and plugged it into everything with a balanced input. The Bass-o-matic played nicely with everything we tried which is not always the case with even professional gear.
Don