This is a really great question. Before I go any further, I just want to say I love your website and store, particularly the vibe, layout, and imagery.
Something to note is an upcoming product update for selling in multi-currency which will essentially allow you to sell to customers across the world in their own currencies that will carry on through the entire checkout experience. There is no specific date for it yet, but there is a blog post from the product team at Shopify discussing it in more detail here.
Regarding your question about having to set up a new tax ID and bank accounts. Another new feature recently released by Shopify was released which can greatly help you with this. What it enables you to do is have every store set to a US address (for example). This would mean that all the stores would payout to you in USD meaning you would only need one US bank account and tax ID which could work across all the stores. It also would allow you to sell to customers in different currencies should you wish. Shopify has a very helpful document on this going through everything in further detail which you can see here.
I hope this helps and answers your question. Don't hesitate to ask should you have any more.
All the best, Nick
Nick | Community Moderator @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog