OK, let's see if we can keep things on topic.
Is it a common layout for the volume control and tone switch, or tone controls, to sit between two gain stages?
Yes, this is typical of almost every Fender design, and many, many other amps as well. Tweed amps all have the gain/volume control and the tone control between the first and second stages. Most blackface amps have the tone stack between the first two stages. The Bassman and Hot Rod series have the tone stack after two gain stages, then a tone stack recovery stage.
Some other amp designs don't have a "stack" of resistors and capacitors to set the tone, but distribute the functions around the amp. You can, for instance, control the treble with adjustable bypass around one of the preamp cathode caps. And you can control bass response by changing the amount of coupling in a late stage, just before the phase inverter.