New Stellaris player has some questions -What are the best empire builds?

Ethics, Traits, Civics, etc
 I usually go democratic-&gt;life seeded+beacon of liberty-&gt;egalitarian + fanatic materialist-&gt; Intelligent, Thrifty, traditional, sedentary, non adaptive 

-How far (in terms of systems) should I expand? 
I often find my fleets overstretched and pirates constantly harassing my outer systems. Should I be building buildings instead of mining stations?

-Fleet power throughout game
What should be my relative fleet power throughout the game, so that I'm not falling behind AI empires' fleet power but I'm also not bleeding myself dry of energy + minerals

-Positioning of fleets during war
Should I draw fleets from other parts of my empire to fight in the war? Also which systems should I capture/station my fleet in first?