>> If I go T/C, which bank do I have to find or is there one in T1 at Narita?

Several currency exchange counters by the banks at the terminal, all similar rates

>> There's a Costco there?! BRINGING MY CARD!

I've been to the one in Kawasaki. You have to take the train and then a local bus. Somewhat tricky if you don't know Japanese when doing the bus.

You can ship your loot back to your hotel or airport for cheap.

>> Is 92,000JPY enough for two weeks?

I typically cash 40 - 50k upon arrival and pile all expenses to credit cards as much as possible.