I hadn't thought about using an execute as, I'll look into that.

The trigger itself does use ORIGINAL_LOGIN() to find the current connection count for the user in the table (trigger's not been implemented yet.)

As for keeping track of the connection count, I've been running a variation of the query I plan to use to populate the table for the last couple weeks, recording the counts and the time it was checked, so I've got a fairly decent general idea as to the max connections someone is using.