you can't escape dividend and capital gains tax as long as you trade any stocks on any US exchanges. The tax advantage you gain as a non-US citizen/PR is primarily centered on USD treasuires, bonds and CDs (uncle sam leaves you alone if you are an overseas investor). Another tax advantage you gain is on buying mutual funds NOT domiciled in the US. You need to weigh the advantages of lower-fee (buy mutual funds available in US) against your marginal tax rate (buy mutual funds available elsewhere) to see which option offers more advantage.
HK is a great place for trading forex, almost every single major bank offers real-time forex trading facility, and the spread is good for retail customers. For more exotic currencies, perhaps you need to call HSBC up to see if they can point you anywhere. Hope that helps.
