For flying, your "good" options are somewhat limited. Pidgeot is a great addition to any team up to the elite four. It's speedy, and has a decent attack, but it's no Staraptor if you've played Diamond and Pearl. You'll find that it (and Nidoking) won't maintain their usefulness very long (kinda like Raticate, if you've ever used one).
Fire you have lined up pretty solidly - Typhlosion. It's pure fire, which limits weaknesses, and has strong stats all around (it's a starter, after all). If you decided to drop it, you could pick up a Houndoom, but that's after the elite four (route
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Water has a ton of choices, with Vaporeon being the best but procuring a Water Stone is a bit difficult. You have to get really lucky with a call back from any one of the trainers who offer numbers and give gifts (I think her name was Lass Dana? On the route west of Ecruteak..) If not, and if you're looking to keep a surfer, get a SATK based water, ie not Gyarados or Kingler.
Dark, especially pure dark, is a bit redundant if you are for sure keeping Gengar (as you should, it's fucking amazing). Also, you'd have to get your Eevee's happiness to max and level it up during the night hours. It's annoying, and Espeon is better of the two if you're going to put the effort in (best psychic until Mewtwo). If you're dead-set on Dark, wait for Houndoom and it will fill two quotas.
So your team would be: Gengar, Nidoking, Typhlosion, Vaporeon, Pidgeot, and Umbreon/Espeon. Pretty good.
