The greatest potential for going from 25,000g to the gold cap of 214748g is transferring servers. However, this also presents the greatest risk and needs the most preparation. First off, transferring costs money. If you go to a server, transferring back as soon as the cool down is up is expensive and impractical. You should look for a server that you can stay on for at least 6 months to a year before transferring back with your huge profit. However, the maximum amount of gold that a max character can transfer is only 20,000. Therefore, you need to purchase goods that are going to net you the most profit when you go to sell them on the new server's auction house. Primarily, these are enchanting mats, but can also be BoE epics depending on the two servers. Before making a risky decision such as transferring, consult the questions below.
Get exalted reputation with every faction you can. This relates to the previous two pretty directly. Gaining reputation with most of the factions of Kul Tiras and Zandalar will allow them to sell you high-level gear, while gaining reputation with the Champions of Azeroth faction will grant you levels for your Heart of Azeroth, the neck piece where all of your AP is stored.
Battle for Azeroth, despite the endless grind, has been an exciting expansion this far. However, raids and additional content are what makes the game great. Blizzard has made the entry level into the new expansion welcoming for new players and some die-hard critics have shared their concerns with the current direction Blizzard are going with making the gaming “easier.”
Kul Tiran human (8.1.5) - "Kul Tiras was founded by fearless explorers who sailed uncharted waters in search of adventure. As a key member of the Alliance of Lordaeron, the Kul Tiran navy dominated the seas of Azeroth with its legendary fleet. But after years of turmoil and hardship, the kingdom grew isolated and vulnerable to dark influences. Thanks to the help of brave heroes, House Proudmoore has been restored and Kul Tiras is poised to fight alongside the valiant Alliance once more."
A "stat squish" and "item squish" was implemented to lower the numbers used in the game, e.g. a legendary item previously with a level of 1000 reduced to 265. Unique class-specific buffs are added back, i.e. mages' Arcane Brilliance and priests' Mark of Fortitude. Titanforging—a random event that raises the initial item level of an item gained via drops or rewards—is still in the game; however, if the item is one of those affected by the Heart of Azeroth, then that item cannot be titanforged.
From “The Burning Crusade” expansion, weapons like Klinge der Zauberei, Die Nachtklinge and recipes for different weapons are really valuable. The best example is Pläne: Teufelsstahlangschwert, worth 500.000+ Gold. These items are World Drops, you can find them in all raids and dungeons. I don’t know any Open World Drops, but that does not mean there are none. Another great transmog source are world bosses and rare spawns on Outland.