Generally speaking, I think it would be a mistake to set up a international subsidiary, or deal with banks in other jurisdictions, in the early days of a startups life. When the millions start rolling in you can consider doing tax planning, but not before.
Having an offshore bank carries negative connotations in some circles -- i.e. the tax man, and certain customers, could feel negative towards your company if they become aware of this.
The merchant account thing is a US (or US plus some other countries) thing. Other countries have different structures, and payment gateways operators who are adapted to this. I think you can get payment processing almost everywhere nowadays.
You could open a new question, "How do I get payment processing in country X?".