You definitely get at least 3 a day (I've gotten 3 today so far).
With the current math, you would never get 24000 rough AD per character, per day, from just Invoking, so you'd never hit the cap you mention. The "insanely rich" part would have to do with the sheer quantity of toons doing the invoking. 1000 characters per day earning 500/day is 5million/day.
Your point about the low numbers (4-500 for low level characters) is valid, but even a level 60 can only get about 2000/day.
How long does it take to get a character up to level 11? I know most people would be faster at this than me, but even I can get there without too much effort/time.
As for taking a hit transferring AD, may I introduce you to the [Jeweled Idol] ?
All in all you raise several valid points, but nothing that can't be overcome. The main point, however, is that the OP's original intent I assume was looking at a mass botting/automation situation, so the invested time would be one time only, up front, per character. After that, it's a script that logs them in once an hour.
I think in the business world that is known as "passive income"
+rep to yo for your valid points