Yeah, I grinded the Wall of Flesh three or four times to get the clock work rifle, made 600 cursed bullets and used the last of my stars in the star cannon and finally beat the twins. Destroyer next, I'll probably go look for strategies for that one.
Probably the easiest method for fighting the Destroyer, albeit a little bit in a cheaty manner, is to build a platform at some height above the ground.
The Destroyer can only jump out of the ground so high, meaning it can't touch you while you can shoot down at it.
You have to handle the orbs that it releases, but these aren't too difficult with a shotgun and some explosive ammo.
And then you can also set up a heart-statue timer to give yourself some regular little burts of health.