I am still trying to figure out the best format for instructions, and it looks like they will have variable length verbs. For a store command, I think one flag digit and five destination digits are sufficient, and allow for a ten digit binary value. When we are copying values between devices, a total of ten digits are required to identify the two devices. For something like an increment command, we only need five digits for the target... but we have room for two, and it might be useful for syncing counters (coping a range of values from EEPROM to SRAM, for example) so why not allow up to two counters to increment at a time?
This is all subject to change, but working through possible instruction structures is definitely useful.