I tried looking for one but couldn't find it. In short: stock fluctuations are random( they follow trends based on seed), stock capacity limit expansion is exponential( not worth it), once you make a net profit of 25k points(like in real casinos) you're kicked out and forbidden to ever partake again in the stock game.
Last point was to limit points inflaction or something.  It was fun to play in the stock market. In hindsight I wish tim made it more like an idle game were you could cash out stock profit for points at diminishing returns but I doubt it's going to change anytime soon :(

It works like a business where you pay tax of your profit. I think we all know that's revenue minus expenses, so going by that, you can keep your "profit" below 25k and keep buying and selling stocks. You can, or in your case, could, use it to slowly pile up a ton of stocks and sell in one massive go. I did that long ago. Nothing crazy, but got 113k/25k earning from that.

It would be fun with a virtual one, where you can keep buying and selling but for a completely useless currency which serves no other purpose than having fun with the stocks.