To keep your open positions from being closed involuntarily, you must make sure your account equity does not drop below the margin requirements.
Margin requirements on demo accounts are the same as on live accounts.
The notional value of open positions on your account is calculated separately for each group of trading instruments (FX Majors, FX Minors, FX Exotics, FX Special, Spot Metals). In other words, when looking at the table, you should read "Notional Value" as the total notional value of open positions on instruments in the selected group, not as the total notional value of all open positions on your account. Opening or closing a position on an instrument in one group will have no effect on the leverage applied to positions in other instrument groups.
The range for Standard and ecn.mt4 accounts is from 1:1 to 1:1000.