For armor you'll want the Molten armor. It is the best pre-hardmode set and is very helpful even a little ways into hardmode. Of course, in order to get it you'll need to get lots and lots of Hellstone bars, so I recommend getting a few obsidian skin potions so you can swim around in lava and get it in no time.
For weapons, you may want a sword because you could get close to the WoF to attack, so I'd recommend the Fiery Greatsword. Again, made with Hellstone bars, but if you have obsidian skin potions it's not a problem. For range though, the Minishark works very well. For ammo you can just use Silver Bullets.
There are so many possibilities for combinations of accessories, so you may have to find those yourself, but what helped me to defeat the WoF was an Obsidian Shield and the Hermes Boots. Make sure to make a long path you can run on in the underworld so you don't have to worry about getting stuck while fighting him.