Do you need to buy a controller to play nintendo 64 emulator games?
It’s better to get a controller, but I beat the Legend of Zelda: Ocarina of Time (with Project 64 emulator) using keyboard. I had no problems with that, except if you need to move the analog stick slowly, which is not possible using a keyboard of course. But Project 64 has the option to solve that. So yes, you can play it using the keyboard.