So I was thinking about what team I'll be using for when I start battling friends and maybe even online sometimes; Anyway here's the team I'm thinking about. Sorry I'm not putting move sets up, but I'm not even done leveling so yeah.
  Gengar
  Houndoom
  Jolteon
  Dragonite
  Tyranitar
  Kingdra
What do ya guys think? Is there any big holes in that team I should know about? Oh and if anyone want's to suggest any move sets I'm open. thanks

You'll run into problems with anything that can learn both Ice and Ground attacks. (Electivire, Claydol, Mamoswine etc.) as four members of your team will likely be OHKO against either of those attacks, and Gengar hasn't got the best defenses and most good STAB'd moves from something with a high attack/special attack stat could likely OHKO anyway, or at least definitely a 2HKO. 
 
I'd also recommend putting something a little defensive in there, you don't really have anything there that could switch into a neutral attack safely, you'd be relying on resistances a lot, which you've not really got much of there.

It looks like ground could pretty easily wreck your shit. If anyone could be replaced, I'd say it's Houndoom. His moveset isn't great, and Tyranitar can cover your Dark moves. If you really want a fire type for your team, I would recommend Infernape, otherwise I would throw in something that could take a hit or two like a Snorlax or Skarmory.

If your doing it for casual battles against friends I think its pretty decent, but in serious battle I think that dragonite and tyranitar are considers ubers or maybe thats garchomp im not sure.  But it all depends on their stats and the attacks you teach them.  Gengar should fair off pretty good, jolteon is like the second fastest non legend pokemon so you'll always have speed on your side, kingdras pretty balanced but there might be better water pokemon, and houndoom may be the one you should change because i think it has relatively low stats.  Dragonite and Tyranitar are bothe great so youll have no problems with them. Try also teaching your pokemon moves that would be effective against the type good against them for example teach a gyrados ground moves to fight electric types. You could also EV train them to boost their stats but only if your really into that sort of thing.

LoL i'm not even sure what   EV training means. I"ll have to look into it.