Heirlooms. At the bare minimum you make sure all the armor pieces upgraded to 110, since this is the lion's share of your experience increase. Neck and Ring upgrades are secondary, but still important due to being able to enchant them. Trinkets can't be enchanted, but you'll want them at max as well, if only to save time by not having to worry about replacing them as you level.
Once you get to about 200g, the theoretical limit of your profit virtually disappears. You now have enough money to start mass buying and reselling those players' goods who undercut everything by an extreme amount. Enchant mats are still a very good focus during this period, especially essences and crystals. You can now afford to buy several maelstrom and abyss crystals and wait until prices fluctuate to resell for a profit. A major strategy you can begin to employ is the multi-character trading and auctioning. If you come across 5 abyss crystals, get onto one character during peak hours and advertise a price 25-50% higher than average. When no one responds to this, quickly switch to another toon and offer the same 5 crystals for 10% lower than before. This will help to raise the median price because other sellers see what they may be able to get for their good. While they are cancelling and reposting, take this time to undercut their new prices, which is now more than you ever could have gotten before when prices were low. If you master this with BoE epics or more rare items, then you can make differences of thousands of gold.
Allied races are variants of existing races. The Void Elves are a version of Night Elves, while the Highmount Tauren are, you guessed it, a version of the Tauren. Four allied races are already in the game before launch and two more, the Dark Iron Dwarves and Mag’har Orcs, were added after Battle for Azeroth launched. Each Allied Race has its own racial abilities. You can also unlock a heritage armor set by leveling any Allied Race to the level cap.
The most simple thing is TradeSkillMaster. This AddOn shows you quite an amount of information in the items tooltip. In my opinion, DBRegionMarketAvg the best source. It tells me the price, an item was posted on all EU realms in the last 14 days. Why not DBMarket? DBMarket only shows you the items value from your server in the last 14 days. This value often gets manipulated. Some people start to post an item with a 500g value for 500.000 Gold on the auction house for several weaks. As a consequence, DBMarket is rising towards 500.000 Gold.  If you use DBMarket with 100% and post your item for 500.000 Gold, nobody will buy it.