Standard format for custom symbols in schematic drawings?
You draw symbol the way your circuit is best readable and understandable. Techniques used are:


grouping pins into busses;
having space between pins groups per their purpose, usage or their connect destination;
making comprehensive labels on the pins and on the devices.


From my experience reading circuits drawn using packages is a nightmare. Packages belong to board layout, not to schematic diagrams.

You may also find drawing circuit diagrams using packages inconvenient. There's always a choice for new device: make quick shortcut and reuse existing package as symbol, or draw own symbol, which takes time and real knowledge of device operation and pin purpose. I used to take time and draw new comprehensive symbol, and split large devices into logical blocks (symbols) for readability.