I actually started work on a spreadsheet to add new robin RD and resources to the base game. I also purchased some wooden barrels in micro size from Hobby Lobby, bought extra Airfix and Zvezda samurai, and an old copy of Shogun for the pieces.
Some great alternative rules sets are out there.
Hit me up in PM is you want to collaborate.
Simple version of marriage rules (adapted from my Conquest of the Empire Dynastic rules):
Game is divided into a number of “eras”. In COTE these are delineated by the inflation events, in Shogun players must agree a number of turns constituting an Era. Each player has a female noble piece in their own colour; think of her as a daughter or sister of your leading noble. At the beginning of each era there is a diplomatic phase in which players can negotiate a marriage contract between their female character and a Diamo (nominally the leader) of another player.
Players whose characters are married to each other have a binding alliance and cannot attack each other. The alliance lasts as long as the marriage OR till the end of the current era (after which it is considered that power has passed to the next generation.)
The only exception is that allies are free to use the ninja to attempt assassinations against their ally’s Diamo. This is a swift way to terminate an alliance that has fulfilled its purpose.
The rules can go deeper, for example birth rolls for female characters in which they may give birth to new Diamo for the succeeding era, or die in childbirth ending their marriage and thus the constituent alliance.
In the medieval version, female characters also inherit lands on the extinction of male family members, but as I understand it this is not really applicable to Japan as multiple wives meant no clans were ever without male heirs.
Note that only a player’s nominated leading Diamo can be married; hence a player can have only two active allies at a time.
Since marriage in Japan was rather different than Roman or Medieval Europe its possible to consider alternative rules such as a Diamo having several wives, or your leading Diamo (and hence active alliance) being determined by rank and hence liable to change mid-era.
Note: The Caesar (not Airfix!) set has an appropriate female figure.