Honestly, sins seem to be quite easy enough.
For speedy colonization, build akkan first. You get one free capital each game. So build that capital dock first then an akkan or whatever else you wanna build first. capitals dogpiling you, nothing much you can do about it except build those repair docks and attempt to outlast them if they're attacking you and your home planet.
Cobalts is really fragile but is available immediately, they're the conscripts of tec. Advantages of cobalts is that they're easy to build reswise. Those javelins is difficult to amass quickly early in the game unless you snagged a 4 crystal icy world next to you.
Its great to have fighter protection. I like building 4 hangar docks per world if possible. Not super early in game, no, but after some res gets rolling, yes.
Astroid fields is protected by 2 militia on normal and easy too i believe. u need like 5 cobalts to colonize it, with an frig or akkan whatever.
And Militia defended planets, how much you'lll need varies. 10-20 for overpowering them quickly.
One nice thing about akkans is that you can basically cast armistice to buy yourself time. lvl 6 akkan required i believe. I've used akkans to race trhough an defended planet to reach an planet of mine under siege before. had like 3 akkans in that game
Other thing, don't underestimate those dunovs.. i learned that they're awesome for kicking strikecrafts around. i see 8+ bombers heading for my capitols I target a random nearby enemy structure or ship and zap it, and watch those bombers crash n burn on the magnetized object, you can magnetize enemy ships too.
Even Kols is easy to spam with a flux field set up If your kols happens to get focusfired, it can tank quite good. If its lvl 6, pop the finest hour then pop phase field 2nd to get antimatter moving as quickly as possible. and spam that phase field til kol lives or dies. Well, not sure on what happened to you but it happens. I was focusteamed upon by enemy once cuz i just had to colonize that pretty terran planet in outer star systems that enemy also had eyes on cuz its pretty.
be active in your defense, even when your stuff gets blown up , build new stuff! be daring, don't be afraid to set up a new repair dock in middle of firezone between ur ships and enemies. one of the stuffs that let me outlast the ai.