Here's the thing about these big money making opportunities in Sims 3. What are you gonna do with that much money? And if you are going to try to get that much money using some extreme method, why not just use the money cheats, because what you're getting is almost like a cheat anyway.
The way I see it is this, true, you will never have any need for that much money. In all realistic terms, what this does is essentially turning on a switch that makes the build tools go into free mode. It also displays the limits of the money in the game as well as displays that they are attainable.
As for using money cheats, I prefer not to use cheat codes or mods unless it is necessary to bypass a design flaw or glitch in the game, the most glaring of which are half height walls to create split level homes, or resetting sims that are stuck for some reason. Not to mention that using cheat codes to create this level of wealth would require repetition bordering on masochism in my mind, similar to start-stopping performances for the guitar extreme cash Metro wrote about, or the art painting on crack that uses the same start-cancel bending of game mechanics.
The reason I keep writing about it is because of the interest some people have to remove the financial constraints without going into sandbox mode.
As for how long does it take? I have made bars over 1 billion simoleans with a single trip each to France and Egypt. I spent every waking moment collecting metals & gems while I was on the trips. Just make sure to create a Supernovium bar to get the process started. So you should be able to achieve financial security within a week.