It sounds like you have the right idea, but here's some tips or suggestions. Buff potions definitely help, and also you will want to make sure you are using the Greater Health Potions, not the lesser ones of course.
If you haven't done so already, I suggest you try making a very long bridge. It doesn't have to be completely flat but at least enough that it's very easily traverse-able and you won't get stuck somewhere by accident or fall into lava. You'll want to focus more on the battle than trying to get around down there.
My weapon of choice for this battle would be one of the flails (Or any big Sword such as Night's Edge) for the numerous mini enemies attached to the wall. Flails take them out easily and quite efficiently since you can hit almost all of them at once. Once those are all done for, this is when switching to the minishark is a good idea. It puts out lots of damage very quickly, obviously, plus the bonus ability to save ammo every-time you shoot it. If you have the Goblin Tinkerer I suggest you put some money in reforging weapons for better stats, not necessary but makes a very noticeable impact when you get a good one.
As for your accessories, you might want rocket/specter boots to get around easier; a cobalt/obsidian shield so you aren't knocked around or into lava, and also in case there any exposed hellstone you could accidentally walk onto; and a Band of Regeneration to quickly recover lost HP. The other two are up to your preference really. I would also suggest reforging these to try and get the Warding prefix (+4 defense). Again not necessary but it will help tremendously in the long run. Especially since having 5 warding accessories means +20 defense.
You can also try to focus on magic items to defeat it. A Vilethorn also makes quick work of the smaller enemies while a space gun (with full meteor armor) will constantly damage the actual Wall without ever using mana. A Demon Scythe is definitely my favorite weapon to use against it though. It will hit everything it passes through, and while it's "charging up", the boss can be directly over it getting hit 3-5 times guaranteed. The only problem is how hard is can sometimes be to find.
If you do decide to use magic items make sure you have a full 200 Max Mana and some Mana potions as well. Restoration potions can also help here as they give back both mana and HP but will give the "Potion Sickness" debuff on use, unlike regular Mana potions. You can also get a Mana Flower to equip. This will automatically use mana potions for you so that you won't have to worry about how much mana you currently have.
Once you do manage to defeat it the first time, beating it again will just get easier since you will have access to higher tier items.
The Pwnhammer should drop every time you kill the WoF. If it hasn't, you've encountered a bug, try validating local files with Steam to see if that fixes it. Otherwise, you can use an inventory editor like TerrariaViewer or a world editor like TEdit to give yourself the Pwnhammer.
Best Answer
Since you are looking for an answer that is fact based, here are the facts:
The regular amount of damage taken can be expressed by this formula:
Note: the multiplier '0.5' becomes '0.75' for Expert Mode. Same for the next equation.
This applies for the Flesh Knuckles item along with every other item in the game. However, since the Worm Scarf item has a percent damage reduction, the formula for the total damage taken for it is a bit more sophisticated:
Analysing these equations tells us several things.
If you have more then 2x the Defense of the Attack Damage, the damage done will be zero, no matter what items you have. The same applies for Expert mode, except for a different Defense/Attack Damage ratio.
The Worm Scarf will always take more damage off assuming the same level of Defense
After a little bit of analysis, I have determined that, without any other armor or buffs, wearing the Flesh Knuckles will be more effective and take off more damage than the Worm Scarf, up to the point where the incoming damage is equal to 22.58 points of damage. After this point, the Worm Scarf will become much more effective of an item. Here are some examples of this circumstance:
Flesh Knuckles
Damage Blocked = 5.5
Damage Blocked = 5.5
Damage Blocked = 5.5
Worm Scarf
Damage Blocked = 3.36
Damage Blocked = 5.06
Damage Blocked = 5.91
In Conclusion
As you can see, the damage blocked by the Flesh Knuckles is a constant 5.5 damage, and does not depend on the damage of the attack, only on the total defense score (which for our example was 11). Furthermore, we can see that while the worm scarf did not block as much damage while the incoming damage was under 22.58, after it reached that point, it blocked more damage.
It is important to keep in mind that this is just an example, and many in-game situations are far more complex than this one. However, I feel as though it is safe to say that the Worm Scarf will be far more beneficial to you in the long run, as the percentage (rather than flat) damage reduction will be invaluable.