Hello Justin, I confirm that the Portfolio Demo could be a suitable starting point.
You could provide a "personal" item in COMMAND mode for each user, which carries the user related subset of TableUserView.
Then, at a second level, you could provide an item for each row in TableB;
these items may be subscribed to by multiple users.

The overload of each item depends mainly on the related update activity;
in principle, 10000 items are not expected to pose any problems.
The unsubscription is also not a problem; when the last client unsubscribes, the Server is supposed to send "unsubscribe" to the Data Adapter and discard any memory associated to the item.
If you notice anything different, please provide us with more details.

The use of multiple Data Adapters was made available to manage subsets of items of different sources;
we didn't think of it as a mean of distributing the load among multiple Data Adapter instances.
If you feel you need to do this, consider that the Data Adapter instance is part of each subscription, hence the client application, when subscribing to the user-related items, should already know or be informed of which Data Adapter is involved.