http://travel.state.gov/travel/cis_pa_tw/cis/cis_1113.html1.) No on Visa or Debit. It's a poor country where as much commerce is barter as currency-based. Most places will not accept US currency and legitimate/reputable exchange locations are rare. Don't carry large amounts of cash. The primary Western-targeted crime is pickpockets. Pretty much all non-trash souvenir items require a permit for export from the government in order to prevent antiquities smuggling, especially of things like crosses(as an ancient base of the Coptic church, some religious artifacts still used today are more than 1500 years old.) Export of coffee, the main crop of Ethiopia is more or less off-limits except to brokers and commodities merchants...which is too bad as it's far and away the best coffee in the world. A pound of real high-grade Sidamo or Yergacheffe is $$$.
2.) Ethiopia is fairly safe though the border regions (to Sudan, Eritrea and Somalia in particular) can be a bit hairy. Likewise, the open-air market in Addis Ababa is a lot like the wild west.
3.) No on Western food unless you're staying close to or in the areas set up to cater to Western businesspeople. That would in some large part defeat the point of going. Don't worry, the local cuisine is yummy...a lot of preserved/spiced meats, a lot of thick stews like Doro Watt(it's a brownish "broken" (meaning of an inconsistent liquid texture) chicken stew.), like most Ethiopian food, it's eaten by scooping it up with a piece of flatbread. Don't drink the water and if you find alcohol of any sort, I'd be shocked. Only eat/drink food in places that look clean...sanitation is not to US standards.
(Never been, preparing for the day when I can go.)