If you evolve Bulbasaur a little later he will learn moves a lot quicker, I usually keep him as Bulbasaur until you get a few decent moves like razor leaf and leech seed, then evolve him. Same with Pikachu because Raichu won't learn as many moves as Pikachu

Good luck, you've not got a bad team, a few pokemon aren't as good as others (Venomoth) but it's personal preference more than anything (good choice on Charizard, Venusaur and Pikachu!)