So far I have:
Venusaur: Level 39
-Cut
-Sleep Powder
-Razor Leaf
- Vine Whip

Kadabra: Level 40
-Psybeam
-Flash
-Confusion
-Psychic

Snorlax: Level 40
-Headbutt
-Body Slam
-Rest
-Surf

Pidgeot: Level 40
-Wing Attack
-Aerial Ace
-Feather Dance
-Fly

Porygon: Level 22 (In Training)
-Tackle
-Conversion
-Recover
-Psybeam

I have just beaten Koga.

~ Who should fill the remaining place and what moves should they know ? ~

Well seeing as this isn't going to be your real team (I hope), I would suggest a Water type, like Gyarados. For moves however, I'm not good with those, especially in your place in the game.

I think Kabutops would be good to fill the remaining place, what does everyone else think?

I say u better switch ur pidgeot with Arcanine or Ninetales U lack a fire pokemon
Moves for Arcanine
Over heat
Extremespeed
Irontail
Flamethrower
For Ninetales
Flamethrower
Confuse ray
Irontail
Grudge
Or if u dont wanna switch than at least remove fly with sand attack
coz u shud never put in fly at ur attacking pokemon coz it gives chance to ur opponent to switch to a resistant pokemon like onix or Golem
As for ur last pokemon put in a water type
Gyarados or Kingdra
Moves for Gyarados
Dragon dance
Hydro pump
Thunder wave
Earthquake
For Kingdra
Hydro pump
Ice beam
Dragon dance
surf
I suggest to really switch ur pidgeot coz it is low in defense PLZ do consider ur team it is a weak team try putting in some good pokemon

Thanks alot. I might scrap the Kabutops as Kabuto is hard to train and replace it with a Ninetails

Good thikin buddy;)

i say scrap porygon you already have a phychic put in fire and water pkmn like a ninetails(above post)and a plolywhirl

Ninetales is a very wise choice, it's a great pokemon!

*and i'm not just saying that