There is only one server, so that makes that choice a bit easier
You need to be AFAIK level 6 (though some say 5, I dunno) on the Fed side before you can make a Klingon character. So I'm affraid you'll have to can that idea for the first few hours. On the bright side, the Klingon starts at that level too, so it's not entirely a loss.
Finally, there isn't much to do on the Klingon side than PvP and a couple of repeatable fleet actions. Which is really why the Klingon faction doesn't have many players. Whether that's what you want or not, only you can decide.
they were probably nearing bankruptcy... which tends to make people 'forget'
Ok so they looking for a quick influx of cash....got ya. Hope they develop the klingon side or even bring in the Romulans or something like that. Played **** since release and the 3 side war is amazing, even today.
After you hit lvl 6 in Fed you can roll up a Klingon, or one of their subservient races, like Gorn, Orion, Naussicaan or you can create your own race. The Klingon starts out as lvl 5, and you have to do some simple and quick 'run around and learn the place' quests before you get to fight. Sort of a mini tutorial.
From there, you can either engage in PvE against NPC Fed fleets or head straight to PvP against other Klingons or Feds. You have to click a button to enter the PvP queu, which as a Klingon has a very low timer; Klingons are usually outnumbered.
Ok so I start as a federation....(weird) then I can become klingon? I'm more of a pvp person myself so that appeals to me. Did they forget about the Klingon content or something?
I usually jump back over to my Fed character to play pve. Anytime I want to play pvp I go to my klingon characters. I created two so I could specialize in ground combat and space and even took on different classes so that may be something you'll want to consider as well. My ground Klingon can take on space pvp pretty well so I can still jump back and forth between space and ground without nerfing myself.