While I have not done the Savings Bond option, the direct deposit is simply for your readjustment allowance and/or cash-in-lieu at the end of your service (for some countries, I have heard they only give a check for cash-in-lieu).
It is not for your living allowance. Once you are in country, the PC will help you set up a local bank account and you will get your allowance directly deposited into that account.
For the forms in the New Volunteer Portal, you should put in whichever bank you use in the US.
EDIT: I should add, the bank should be one you can access while traveling/overseas, as you may need to access the readjustment allowance while on a CoS trip (assuming you take one).