It is my understanding that the Mercere have taken up the Florentine and Templar practice of “banking” and “accounting.” We have a covenant heavy in Venetian and Mercere influences. We are thinking about “banking” our vis as part of the covenant charter. (Instead of a salary, or holding all in common, using a system of deposits and withdrawals, getting credit for what you put in and withdrawing only when used.) Does anyone have experience with that? How did it work?
We generally do this but we use a mixed system of a low annual vis allotment, IIRC 2p of any type, and a possible season of service to the covenant that can be done once every two years that earns more vis, 4p. we don't worry about interest or anything, people just get a credit to their account when "earned" and their account is debited when they withdraw for their projects.
If you are talking more like the investment accounts from HoH:TL I haven't really explored that in game. I built a redcap Companion around it once but we never really got to that part of play.