Miniatures Rules: Movement Trays and Unit Size

I'm starting to put together a set of miniatures rules for the side game.   My goal is to get a system that is fast and playable, with as little math and figuring as possible.  

Gygax and Perrin's Chainmail, is a good start, but gets all bogged down in the post-melee morale phase.   Tony Bath's two systems from the 60's are also pretty good, but also have some fiddly bits in the morale department.    Pig Wars was always fun, but I'd like to get away from the playing cards system.  Also, movement is handled by individual figure, and I'd like to do unit movement.  Warhammer Ancients is more detail than I want to get into, and is too historically specific for our needs.  The WRG systems and DBM systems by Phil Barker are far too fiddly for what I want to do.

I'm also looking to make the system fit my particular miniatures collection and system (so I don't need rules for Elephants and Chariots), and I want a system where individual figures are removed to indicate casualties.

My first step is Basing Units.  I want to use a standard sized unit Movement Tray, and thought that 4x6 would be ideal.    Here's my first step:

UNITS AND FIGURE BASING

INFANTRY:

Each Infantry Battalion is mounted on a single movement tray that measures 4 inches by 6 inches.

A Battalion must contain at least 6 figures and no more than 24 figures. If casualties ever reduce the number of figures to 5 or less, the unit breaks and flees the battle field or surrenders.

MISSILE TROOPS

Each Battalion of Archers, Crossbowmen, Slingers or Javelin-men is mounted on a single movement tray that measures 4 inches by 6 inches. Each Battalion must contain at least 4 figures but not more than 18 figures. If casualties ever reduce the number of figures to 3 or less, the unit breaks and flees the battle-field or surrenders.

SHOCK CAVALRY

Each Troop of Shock/Melee Cavalry is mounted on a single movement tray that measures 4 inches by 6 inches. Each Troop must contain at least 4 figures, but no more than 8 figures. If casualties ever reduce the number of figures to 3 or less, the unit breaks and flees the battlefield or surrenders.

SKIRMISH CAVALRY

Each Troop of Horse Archers or Javelin Cavalry is mounted on a single movement tray that measures 4 inches by 6 inches. Each Troop must contain at least 2 figures, but no more than 8 figures. If casualties ever reduce the number to a single figure the unit breaks and flees the battlefield or surrenders.