This is concept of banking mod.   There would be 2 banking system: simple, extended. In simple system there would be one account to all holds. For extended system, every hold would have  separately account. At the start there would be npc in every jarl palace to manage accounts.    Account types : normal account - you'll locate gold in account without any profit. gold can be stolen  but you can buy insurance for it for 10 gold per day investment account -