Money. The currency is the West African CFA franc (XOF), pegged to the euro at 655.957 CFA to 1 euro. ATMs are available in Cotonou and other major towns but can be unreliable -- bring euros or US dollars as backup. Ecobank and Bank of Africa ATMs tend to work best with international cards. Outside the cities, cash is king. Credit cards are accepted almost nowhere except a few upmarket hotels in Cotonou.
Language. French is the official language and the one you need. English is almost nonexistent outside a handful of hotels in Cotonou. In the south, Fon and Yoruba are the most widely spoken local languages. The north has at least six major languages including Bariba and Dendi. A few words of French will go a long way; without any, you will struggle.
Safety. Benin is one of the safer countries in West Africa. Violent crime against travelers is rare, though petty theft and pickpocketing occur in Cotonou markets and around the port area. The main risks are road accidents -- drive or ride defensively, especially at night. The north near the borders with Burkina Faso and Niger has seen some security concerns related to the wider Sahel instability; check current advisories before heading to Pendjari or the far north.
Health. Yellow fever vaccination is required for entry. Malaria is present throughout the country year-round -- take prophylaxis and use mosquito nets. Tap water is not safe to drink; bottled water is widely available and cheap. Medical facilities are limited outside Cotonou. Travel insurance with medical evacuation coverage is strongly recommended.
Electricity. 220V, 50Hz. Plugs are the European two-pin round type (Type C and E). Power cuts are common outside Cotonou, so a headlamp or flashlight is useful.
Communications. MTN and Moov are the main mobile operators. SIM cards are cheap and easy to buy with a passport. Mobile data coverage is decent in the south and along main highways, spotty elsewhere. Wi-Fi is available in hotels in Cotonou but rarely reliable.
Tipping. Not expected but appreciated. Rounding up a taxi fare or leaving 500-1000 CFA at a restaurant is generous by local standards.