The best Pokemon Leaf Green team.

[Arjahn]

I just beat the Elite Four the other day on my Nuzlocke run using the following:
Magneton, 52
Kingler 51
Marowhak 49
Charizard 50
Dodrio 49
Victribell, 52

I'm telling you, Adamant Kingler and Modest Magneton clean house.

[omid]

If you can get it, and that's a very big IF, go for a Dragonite, they are extremely hard to get but it all pays off in the Elite 4.

Other than that, your Squirtle is fine. Maybe get a Raichu, I personally love Snorlax and Nidoking, and because your playing Leafgreen, get a Sneasel (exclusive to LeafGreen).