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.
If there would be a transmog server #1, all transmog vendors would transfer there and the market would get destroyed fairly quick. In general, Roleplay-Servers like Argent Dawn or The Aldor are better server for selling transmog. On high pop servers you have a lot of other players selling stuff and as a result, low prices. On low pop servers prices are acceptable, but you have no buyers. So there is not recommendation for a server really. Its up to you.
After completing your island expedition and second foothold, head back out to your third and final zone to quest in. Note that any legendaries you were using to level have become inactive and are merely stat sticks now. Feel free to replace them with quest gear as you obtain it. Before heading out, feel free to send your three champions out on new missions!
5. at least get 4 characters with these professions. Tailoring/Enchanter; Minning/jewelcrating; Minning/Blacksmithing and Herbalist/alchemist. You can skip blacksmithing and take Minning/herbalist with 1 of your alts. While doing your world quest in argus, try to get all the ores and herbs that you can. Send all the cloth and greens to your tailor character.
For your tank... I'm assuming you meant which race should you be, not which class, since you seem to want to be a warrior! Well, if you were Horde side I'd recommend Tauren for the health buff. But honestly, I *never* pick a race based on the racial features - only based on the flavor. If you are going Alliance side, I am quite partial to dwarf warriors myself but pick whatever seems most fun to you!