you need 1k minimum to trade for 2k. that means your credit is double the deposit you put in.
for foreigners, deposit is compulsory.
my account is DBS TDWaterhouse, you just send the application online then you will receive letter asking you to go down to DBS shentonway to sign some forms. no need any document, just bring passport and student pass.
the deposit can be withdrawn anytime, but you will have no buying credit if you withdraw all you deposit.