I' ve been through all that sh.., so I can help you.
As a non resident alien, you need to fill in the W8-BEN. Don' t mind the SSN and the Individual Taxpayer Identification Number. You don' t need them.
Once your broker gets the W8-BEN, and has then the proof you' re a non resident alien, you' re OK. You don' t have anything to deal with the IRS. The tax laws that will apply are those from the country you are a resident of. The country where you pay your taxes.
The only thing that will be taxed, automatically, by your broker, is any income resulting from the cash sitting on your account (if though your broker pays you income on your cash, they don' t always do it). There is a slight withholding on this, but nothing too big. This is done by your broker, so you don't mind about it.
I called the IRS to know it this was right, ie taxing you on cash income, they said it was. So don' t worry.
You' ll never be asked for a W8-BEN anymore. Once they get it, it' s ok(unless of course, you change your nationality, country of residence and other things that would affect your tax situation).
For what regards margin requirements, and leverage, you' ll be bound to the same terms the US residents are bound to. There not any difference from that point of view. So yes, if your a daytrader, you' ll need $25K.
So it' s not that complicated. Send the W8-BEN, and you' re in order with the IRS. Nothing to deal with them.
