As far as password, you can enter EITHER your brokerage account password or MT account password, or if you setup a trading pin in settings, then you can also enter that.
Trading tab on the chart - MT does not change the values that are entered there - you setup the QTY etc on that trading tab - if you then select buy or sell, it should use whatever is selected in the QTY field on that trading tab as the default, which you can change while the cursor is in Trade Drop mode by just using the mouse wheel