You can't create a sub-account in NZD, SGD, etc., because you can't create a primary account in NZD, SGD, etc. Those are not valid account (primary or sub-) base currencies, which are: AUD, CAD, CHF, EUR, GBP, JPY, USD. Once again, I am not aware of any difference, trading-wize, between your primary account and sub-accounts.
As to trading by transferring funds among sub-accounts denominated in different currencies, yes, your scenario 2 is "a little worse" indeed. According to
this, by around $2.02 per lot per day. Which is 0.0015% a day, or 0.55% a year. Go for it.