I've been playing AI games in Rebellion on medium and hard with unlocked teams, and I'm not seeing the AI gang up on me quite the same way. Maybe I'm getting ships faster then you are and it thinks I'm strong enough to not be an easy target, I'm not sure.
If you're playing as TEC, once you get to 3 worlds you should try to get Trade Ports. They're not a high tech to get (only 2 research stations) and they make a HUGE difference. It doesn't take long for them to pay for themselves, but you don't want to go much further then that until you're more established. Broadcast Stations are nice too, once you can get there (but don't try to rush to them too early). If you turn your capital ship into a fleet when you get it (there's an option to do that in one of the buttons on the ship but I forget which one), you can then set the waypoint on your planet with the ship factory to the fleet and newly constructed ships will automatically fly to and join your fleet. It's a convenient way to build.
If you're finding yourself under attack in the early game, some Cobalt's with your one capital ship are fairly effective at defense. If you unlock Repair Platforms (a single millitary lab), two of those dramatically boost your defenses and they're not very expensive. Don't build a second capital ship until you're more secured, they're expensive and the frigate support will take you farther.
For your one capital ship, the Kol is a better fighter then the Akkan (with the Railgun & Forcefield abilities), but the Akkan means you don't need a colony ship. I prefer the Kol as my first ship personally because it's better at beating early attacks.
Good luck. 
