Do you need a modem besides Wifi router?

This would depend on the Internet provider. Most of the main ones, like att or cox, yes you would need both and you would need to make sure the modem is suited for a cable internet connection. Atlink, another Internet provider, is different where you have to use their modem and they install it, in which case you would only need the router. Also, if you need a router and modem you can buy a combination which has both the modem and router built into one. I thought it was cheaper to buy one item that had both built in, but I had to switch Internet providers when I moved that had to use their modem and then had to buy a separate router because the combination would not work without cable provided Internet, so I would keep that in mind.