1) If you add your own currency, it won't be updated, simply because European central bank provides update for only 32 currencies (that are shown in application)
However, I've received requests for additional currencies, so if you have some web address where fresh exchange rates for your currency is shown, I'll be glad to make an update to application.
2) Application's main focus is on offline users, so yes, it will work even without any data connection (outside hotel, in the desert, even without sim card in flight mode
)