General design questions for multi-stores

I am new to OpenCart and am developing a site for a customer who sells merchandise in two different currencies. It's a long story but we've settled on using the multi-store feature of OpenCart. Each store sells the same categories of merchandise but the products are distinct. One store processes in USD, the other in Yen. The mechanics all work fine but now I am focusing on the customer experience. This customers understand why the currency policy exists and do not need a site to be idiot-proof (thank God!). I have these questions for those that have experience along these lines or can visualize it and offer suggestions:

• I currently have the primary domain set up for USD (the default store) and a subdomain using JPY. Therefore the customer will always land in the USD store first. However, I'm wondering if it is better to have a subdomain for each currency-based store and use the default as an entry point to both. Thoughts?
• If I go with using the primary domain as the landing page only, what is the best Layout to use? At can be as simplistic as two links, one for USD and the other for JPY, along with text explaining why there is a choice.
• For the landing page, should it just be simple HTML?
• Lastly, does anyone have experience or suggestions in making multi-store as user-friendly as possible? Two carts are needed to process two currencies (it comes down to the business owner wanting to freeze exchange rates and not do any conversion) but in a perfect world customers would have visual reminders that there's a separate store if what they are looking for isn't in the current store (or prompt them to make impulse buys even if they found what they were looking for).

I know this is a lot to ask so if there's documentation or a demo that I can review then please point me in that direction!