The single most important thing: if its FUN to obsess over the little bits of fleet design, do it. Because the hardest thing to find in 4x is the one bit that YOU like done correctly. This game has three things going for it that no other game has:
-The capacity to do truly detailed ship design.
-The economic implementation is my favorite part (industrial production delinked from but still associated with ship production; and achieving the logistics of industry, mining, transport, and mining is tricky, and this is what i obsess over),
-You have the option to set to zero NPRs and just economically turtle for a phase if that suits you. No NPRs flying into your systems, appearing when you explore them, while providing the ability to manufacture one if you want one to shoot at.
And thats great. I say, do the role playing thing. Don't worry about your fleet building much til you actually encounter someone who shoots at you. Or, even, would your society arm itself immediatly on discoving precursors? Or would it hang back and explore elsewhere? What about the swarm?
Now that I know the minimums of what is needed to hit a precursor fleet, i'm saving the serious design choices for when I actually encounter something. Should make things a little scary if they're more aggressive than I am in my defense production