In the very early game, I usually run out of resources very quickly. Crystal goes first, but metal is not far behind, as I micromanage and switch to metal-intensive projects when crystal runs out.
And then, I start building starships and turrets, and then crystal is pretty much at 0 all the time.
Next game I play, I'm going to try to just build Mk1 and Mk2 fighters (and maybe some bullet proof fighters as well) early on, then take over some nearby planets while I build my bombers and such.