Don't worry about inflation. You probably had in mind the 1920 inflation in Germany, when money was printed like mad. But trading does normally not cause inflation. Your money won't lose its value. Inflation is caused by a demand/supply imbalance that can be completely unrelated to the money circulating in the financial market.

The financial market can also not be converted to a zero-sum game. Otherwise you had to freeze the exchange rates and prices of all financial assets, which is unrealistic. If the banks and fonds should have been left to die in 2009 is another matter. But I think we did not really have that choice.

As to the question how much money you need, you should have about 20000 EUR in your account for receiving a monthly income in the EUR 1000..2000 range. But this is preliminary, as we're still working on the trade algorithms. It's surprisingly complex to calculate the real income from the income gained in the simulation.

One question, though: isn't buying/selling stocks very expensive? Afaik it costs about 5$ per transaction, which would make trading senseless for less than some million $.

you are not trading stocks here, you are buying and selling moneys of other currencies.

Dagobert does not trade single stocks. It trades currencies, stock indices such as the DAX or NASDAQ, and commodities such as oil or gold.

The usual cost per trade and curreny unit is about 0.0003 $. If you're not Warren Buffett, you normally trade not with millions but in the 100$ range.

ah, I didn't know that. But then, of what time scale do we speak here? How long is one average period of buying and reselling an index?

If the platform you are trading on allows that, avarage period could be a couple of seconds/minutes

Okay. I'm still not sure how you could probably make money out of it. Stock quotes are grey noise, so... well. Without some extremely sophisticated cross-correlation algorithm... how do you expect the average user to model the stock market? If it was that easy, more people would do it.

from sudden changes on parities.

you buy dollars when they are cheap, then sell them back when they got more expensive.

And for finding out when they are cheap and when they will get more expensive, the average user will hopefully use a somewhat more sophisticated algorithm than cross-correlation.

I bet the average user doesn't even know what that is, let alone know how to code it.