The Villagers of Zephyr Town
Besides the 10 marriage candidates, there are 14 other villagers who live in Zephyr Town. These people are often family members of a marriage candidate, or a shopkeeper, or someone who has a specific job in the village. You won't receive any special items for befriending these other villagers, but you can see some random events that give you some back story on the villagers and marriage candidates.
There are some villagers who appear in the game that you can't befriend; Chen, Gannon, Pierre, Wada, Diego, and Enrique. Chen and Gannon can only be found during the bazaar once you upgrade to 25% expansion, and Pierre appears at the cooking festival as well as a bazaar customer with bazaar reputation points. Wada will unlock once you reach year 3 and can always be found at the horse track afterward. Diego and Enrique are also shopkeepers at the bazaar, but you'll see Enrique right from the beginning whereas Diego doesn't appear at the bazaar until you reach the 75% expansion level.
Besides the villagers who have portraits when you talk to them, there are a few sub-villagers who appear in the game. The faceless bazaar vendors can't become your friends and neither can any of your bazaar customers. Once you unlock the horse track area, you'll find some weekly children visitors at the Hotel. Lenny and Trishia stay at the hotel on Wednesdays, while Nessa and Theo stay on Thursdays. On festival days, you'll find all 4 kids in the Hotel lobby.
Town villagers don't have heart color indicators like the marriage candidates (minus Amir and Emiko of course) but you can see how friendly you are towards them by going to the Residents page in the bookcase assets menu. The faceless sub-villagers won't appear in the assets list at all.