Am I responsible for any special state taxes if this is shipped to a USA address and/or duties or customs if this is an overseas order?

Because you're painting will be shipped out from Oregon which does not have state sales tax, in most cases that added expense would not be an issue. However, there are some states that are trying to enact a law that requires the seller to collect sales tax for that state, even though the sale was not consummated in that state. Naturally we are doing our best to keep on top of this and will certainly comply and notify our customers, just as soon as we become aware of any changes or new laws, but we can not be held responsible for any omissions. It is solely the buyer's responsibility for any taxes or charges due that their state or country imposes. 

Any currency conversion rates, taxes and/or duty charges for overseas orders would be confirmed and quoted in US dollars by e-mail.