1) The best PvP gear in the game at the moment is 2 star officer AP gear from Katalam. You can buy it in Danuar Spire/ Kaisinels Beacon in Katalam for AP and Ceramium Medals. These are mostly obtained in The Eternal Bastion, Krotan, Miren and Kysis fortress instances and Ophidan Bridge (you can however also get them from other places, just not as many)
2) You can craft potions and scrolls with Alchemy. Food is made by Cooking. You can gather the materials for the recipes with Essencetapping, or level Aethertapping and morph aether into the materials you need with Morph recipes.
3) Manastones, enchantment stones, godstones and idians. Idians are basicaly temporary enhancements for your weapon that add a few points of certain stats. There are various types of Idians in the game. You can get supplements from some NPC merchants and certain camps in Katalam and Danaria.
4) Normal Stigmas can be bought from NPCs, Trade Broker or dropped from mobs. Greater Stigmas must be bought for AP from NPCs.
5) 4.0 adds 3 new classes, gunner, bard and aethertech. There are also magical Plumes, a kind of accessory that adds HP and attack or magic boost. There are obviously new dungeons and zones, and there is also the Tempering system for accessories (increasing PvP % by using Tempering Solutions on your accessories)
6) It's a pay to skip server. Meaning that you can either pay, or you can grind your way to ultimate gear. You can definitely do whatever you want without dropping a single € on the shop.