"Junk turret" are fun and are a great help especially in solo playing. However, several "junk turrets" should not be active at the same time. The OP comes mainly through it I think.
I think so too, but players should also reach their limits in higher levels of difficulty. To put everything on "junk turret" should not be the way. "Junk turret" should be a good help, but not the main strategy that puts everything into the background.
Increasing the price of ammunition (more iron per shot) only brings more grind.
(Unfortunately, I can only speak very little English. I have used translation program German – English.)