The issue is dynamic config. I could run a hundred and manually config them. I am trying to build something that is more dynamic. Allows for a user to come and go without manual intervention. It seems the advisor account type might be the path. It allows one login across multiple accounts owned by others. Never seen that through the API but TWS and the REST API have it. I can change a dropdown in TWS to use a different account so I know it works and exists. I may use the gateway in that way but a REST API is more appealing from a coding perspective and appears to be the future for IB API access.
IB API has full support to trade a structure (advisor) with any number of linked accounts. In practice under 1 login (port number), you will see all the managed accounts. You can trade them individually, or you can trade them all at the same time from the Fxxx (Advisor) account, by defining one or more "allocation profiles" (allocation profiles can be specified at the level of individual orders, although usually one would at most use distinct profiles per instrument). In addition, there is an additional one, called FxxxA, attached to the Fxxx which they call "Universal" that can summarize all the subaccounts. This is useful to skip multiple calls to the reqAccountUpdates() for instance unless, for some reason, one needs to find out also the realized and unrealized of every single position. But usually, reqPositions() may suffice to check synchronization between your app and the underlying acct (liquidation, expirations, assignment, etc.).