Glad that you�re enjoying the game.
What gottcha from the planet were Weapons Platforms.
I lost 57 ships to 16 dreadnought just Last night, and nearly lost the war. (What saved my *** was having warp point technology. I was able to build (66 turns) two mini warp ships that each had a warp open and close component. I closed the warp points to the sector that had the Dreadnought, now 40 +.
A cheep way to save ones but, but effective. I am now massing a huge armada and will open a warp point to the "infected" system and wipe them out. All of them.
There is no set rule about what to do early on except research and explore. You'll need to expand, but your best friend will be counter Intel. Intel attacks can decimate your empire in only a few turns.
To control rioting, or prevent it, you can place troops on your planets and keep ships in orbit or in the same system.
If a planet begins to riot, you'll have to send in ships (10) to that system, to the rioting planet, and park them in orbit until the uprising is suppressed. (BUILD an urban pacification planet on one planet per system. This will also help keep the rioting down.
As for the dreadnought, chances are they will simply look around and leave. You could engage them, but you'll loose unless your ships are superior.
Shields and armor are utter necessities to have. REASEARCH THEM from the beginning. (May have to research some other tech to get them, so do that too.)
Design specific ships for specific tasks. IE, make a dreadnought with only ONE type of heavy weapon, and be sure to use the proper Mount (upper right hand corner of the ship design window). Add a few Point Defense Guns to each design to counter missiles and fighters.
I use three basic types of Ships.
Battleship (heavy mount) Beams
Dreadnought (heavy mount) Torpedoes
Battlecruiser (medium mount) Point defense
Then Carriers and Destroyers. (Destroyers are armed with proton beams.)
Each of the ships have decent shields and armor.
One other option is to design a small, and cheap to build, escort class. Make them in bulk, and fleet them up. 25 of these against one Dreadnought is a sure in victory, and if you loose, you've only lost the cost of a few ships as opposed to the cost in resources and construction time of much larger ones.
There is a guide thread floating about the forum. Even check out the downloads section for one. There is a ton of useful info in each of them.
Best of luck.
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"We've made too many compromises already, too many retreats! They invade our space and we fall back -- they assimilate entire worlds and we fall back! Not again! The line must be drawn here -- this far, no further! And I will make them pay for what they've done!" -- Captain Picard STNG
New Age Ship Yards