The difference between a Weapon, a Fighting Style, and a Cursed Technique in Kaizen is that these are the three separate combat systems in the game, each with its own moves and progression, and a strong build usually combines all three rather than relying on just one.

You get a Tier 3 Accessory by collecting duplicates of the same Accessory and fusing them together in the Accessories tab, first reaching Tier 2 and then Tier 3.

Yes, you need to reach Level 25 to trade with other players in Kaizen, this level requirement exists specifically to stop the trading economy from being abused by alt accounts.

Yes, you keep the Weapons, Accessories, and Clans included with my purchase, exactly as shown in the listing.