In short, no. Costa Rica uses 110 volt, 60 cycle electricity, same as the US. Plugs are typically the 2 pronged flat type, so US travelers will not typically need a converter or adapter.
Visa and Mastercard are the most widely accepted cards in Costa Rica. However, the likelihood of acceptance decreases the further off-grid you go. Some small restaurants and stores may not accept credit cards. It is encouraged to use the local currency, colones, for small items. Some locations offer discounts for paying cash.
Your passport and it must be valid for 6 months after departure date. No visa is needed.