Fleet Commanders. Get one of these for your nut-cracking fleet. It instantly doubles your hitpoints and boosts logistics too. Nice.
Did they change it recently? Last I checked they doubled the amount of moves on the galaxy map! Which is potentially even bigger than the battle buffs.
I liked xeno/slaver but the slow ship production was painful. Getting "free" citizens was nice too (building population and saving up social mfr, then build citizen in one turn). I ended up with 10 leaders in Ship Construction to help offset the xeno penalty.
When going xeno, you should definitely take the militant +2 trait, too. 70% is a lot more than 50% ship production.
What ideology are you playing with? Try malevolent production, intimidation centers are useless, but the two follow ups solve your ship production by making your homeworld ridiculous.
Take my advice with a pinch of salt, since I played my only godlike game in crusade only up till turn 51. After that I concluded I was winning. I don't know if there was a train still about to hit me, but at that point I had kicked two civs into the dust (colonized 3 worlds, conquered another 11, helps with the ship production weakness, too AND saves administrators), was first in research by a margin and had all the techs I needed to start putting out my workhorse battle ships.
Talking about ships, if you want to go max abuse, don't fool around with defenses, get evasion+repair. It stacks a lot better than normal defenses, because the AI doesn't take counter measures to evasion. 20% evasion from civ trait plus 10% from a jammer, plus 35% from two fleet boosters makes 65%, that means repair and hitpoints are 3 times as strong as they usually would be (against 100% accuracy weapons, against lower it is even more). Ones you ahve high enough drive tech, you add the tactical speed boosters for even more evasion on your frontline ships. Reducing enemy hit chance to 10% (the absolute minimum) and having 10 repair means, they need to effectively do 100 dps in damage to even scratch your ship. Not to mention they still have to eat through 1000+ effective hp (but that's lategame obviously).
I probably would follow it up with beam weapon specializaion, since it allows for high tier weapons construction with low ressource cost.
Lastly, your strongest feature as synthetic is not population, but twin research colony uniques. The others only have civilization uniques.