Mark, I will await your rules with interest .... and am not above stealing good ideas to incorporate into my own

My aim at the moment is to produce a game with a dozen or so units a side, which models my own view of how things may have worked, that is set in the middle 1500's period of the Sengoku Jidai, that models the friction inherent in any battle and also the challenges of commanding troops without radios or even megaphones! Nothing like giving oneself a challenge

I suspect your aims are not radically different!
On cavalry, all the accounts I've read (all secondary sources as I don't read Japanese) of the period I'm aiming for refer to small groups of cavalry attached to the sonae to exploit success or cover failure.
Even the accounts of the supposedly massive Takeda cavalry charge at Nagashino has groups of 30-50 horsemen riding up to the barricades, half a dozen to a dozen being shot off their horse and the rest riding off.
The few stats I've seen show 5% to 15% of samurai armies fighting mounted with the higher percentages being Eastern Japanese clans.
I'm not a big fan of the view that Japanese horses were broken down nags capable of no more than 9mph when loaded. I believe they were small, sturdy and agile. Ideal for raiding, skirmishing, tip and run tactics and pursuits but not for devastating heavy cavalry charges.
As ever, YMMV
