Adamantite is the best armor if I recall. Chunkium increases your reach as a full set bonus, but is worse than Adamantite in terms of defense, unless my knowledge is outdated for the newest update. Power ups are honestly a lot more important as getting good ones can let you survive with only a rock and no armor. Wyvern Dagger is the best weapon because it's high attack speed allows you to proc any power-up ability much easier, such as sniper scope, you obtain it by getting a rare drop from the flying mobs. As for best pure base damage I'm unsure, I would assume Chunky Hammer, if not Gronk's sword, Big Chunk and Gronk drop the respective materials for those weapons.

Stay close to him while circling clockwise for the most part. When he does his flurry of swipes, he'll put both hands up if I recall, you need to sprint to get behind him and out of his range. When he goes to throw his swords, he puts one knee up, just sprint and try to stay as close as possible while circling, if you're close enough neither thrown sword will hit you, although the knee he puts up for the animation makes it a little difficult. Finally, when he does his slam attack, where he puts both swords together, start sprinting directly away from him a little after the animation starts and then jump once you hear the sound effect of it being fully charged, you should hear it just before he actually slams his swords down, and you'll jump right over the projectile. This usually works for me. I'll make a video about it in a day or two if you find the explanation hard to understand.

With the current update it would only be brutally hard if you had to play on gamer difficulty, as big Chunk's damage is far less consequential on easy, but would probably come close to one shotting on gamer. Assuming you tried to fight a Big Chunk boss shrine as soon as possible.

I don't usually run Adamantite%, but this actually seems fun.