Personally, I'd go for at least three in order to make travels easier, ut that's your call. Just know that the fewer Pokémon you pack on the road, the tougher it'll be once you hit the later routes.
[Granted, he stuck with just three for his first few months, so it's not impossible.]
video;
[Granted, he stuck with just three for his first few months, so it's not impossible.]