Heirlooms are special pieces of armor that level up with your character, so they have stats that are always respectable for your character’s level (up to level 110). Heirlooms that fit the head, shoulder, chest, legs, and back armor slot offer an experience bonus. The total bonus is 45 percent if you have them all. It’s also possible to acquire a ring that adds another 5 percent, but you must win a fishing contest acquire it, and that can take some time.
As the first major content release of Battle for Azeroth, patch 8.1: Tides of Vengeance is adding a number of new ways to gear up, as well as increasing the item level of rewards from existing activities. Tides of Vengeance goes live on December 11th and will add most of the new content, but Mythic+ and PvP Season 2 will not start until the new raid, Battle of Dazar'alor, releases in January, at which time the item level thresholds will increase to the new Titanforge cap of 425.
Cooking benefits all classes, especially melee and hunters (it is a free source of food). Until higher levels, the benefits it provides are almost exclusively stamina buffs. While more stamina is always nice, cooking is not essential to leveling. Considering the time investment required, if you pick up skinning then cooking would absolutely be a wise skill to level prior to hitting your level cap, as beasts often drop meat useful for skilling up.
The World of Warcraft API has a list of functions that you can interact with and to talk with WoW using Lua. These are your building blocks for manipulating WoW windows and chat boxes and so forth. Looking at these for the first time can be very daunting. But don't be discouraged. After getting more familiar with Lua the WoW API gets much easier, and the documentation gets much easier to read. Keep in mind there are many different ways to accomplish your goals, so when going though the API keep looking until you find a way that best suits what you need.
But now, the Gear Advisor starts popping up, trying to get me to put the old 360 version Ring #1 into Ring #2's slot, since iLvl 360 is better than 350. Except I can't do that, because of the "Unique-equipped" modifier. So I click "Cancel". And then the window continues to pop up after every action my character takes, over and over and over, until I get rid of the old ring by vendoring, scrapping, or destroying it.