Tips to finish hardcore:
Don't upgrade the base weapon much, the minigun and shotgun are all you'll need, don't buy the rocket launcher either until the end for the upgrade medal.
Don't bother repairing the turrets, it takes too much time and they die within seconds.
Max out the refinery as soon as possible, then get the minigun to lvl 4, engine, plating and nanites to 2-3, torch to 3, get the 1st ship part, max minigun and start sentries dispenser.
Max it out too, only then you should buy and place turrets, only north of the ship, enemies never attack from south. Replace destroyed ones every wave. Then max engine, plating and nanites, get the shotgun and max it out too.
After wave 20 you will definitely want the shotgun maxed for quickly clearing groups and killing tanks. Until then the minigun should be enough.
Ignore the small fast bugs, your turrets will handle them, focus on repairing instead.
As far as I've seen the waves are probably endless, with constantly increasing numbers of enemies. Try to finish before wave 40, after that things start getting messy and you'll barely have time to fix the ship between waves. Heal yourself in the upgrade screen to almost full after each wave and maybe even in between if necessary.
Try to draw away the enemies attention from the ship and turrets, walk backwards in steps to easily kill tanks without them hitting you. Circle ranged enemies while shooting them to avoid getting hit.
It's all easier than it sounds, there's room for variation.