That depends on the chosen smart card technology. Some smart cards are USB devices in themselves, such as YubiKeys or associated FIDO-certified devices. Otherwise, you may want or need a smart card reader to read cards in a similar format to what you see on chip-based credit cards.

USB smart card readers are fairly cheap. Many business-focused laptops have been available with smart card reader options for many years.

Yes, they are cheap though (~$10) and they sell keyboards with built in smart card readers.

Yes.