Well, when I started the game, I chose Cyndaquil, you wont have much of a hard time with Chikorita in battles unless your going up against a Fire Type, or Ice, or I think Flying as well not sure, But you never know what some pokemon may have, for example: If you are battling a Flying Type, that has flamethrower, which I have seen many use lol, you need a good defense for it, it wont do much damage, but it's better to be safe then sorry, unfortunaltiy their are only 2 HMs I believe that Chikorita can use and that is Cut and Strength. As for pokemon to use in your party aside from your starter, try to be as balanced as you can, try to pick out certain ones like I'd say Pidgey is a good Normal Flying to have, he is the one i always use, or if you perfer a 2 toned type like HootHoot which is flying that can use psychic moves which will help against a few gyms and the E4. If I were you I'd try to find a good fighting type, because Whitney is a pain in the butt lol. Now your first Gym is a flying type gym, so Chikorita isn't going to be much help.. I know i'm kind of contridicting myself, but I can't remember is flying is strong or weak against grass.. But like I said, it all depends on what your favorite types are, I'm a mixed/dragon user, it doesn't matter to me what type it is lol. I do however specialize in Dragon and Psychic.
