In addition, you'll want to pick up leg and shoulder enchants and have them in your bags. These enchants have a level requirement of 80/85, but can't be placed on items above iLVL 136. You can get around this by having a level 85-100 character apply the enchant before mailing it to the character you're leveling, thus getting use of the enchants before level 85.
"The way the glyph market works on most realms is that there are a couple of people willing to put in the long hours who will have every available glyph posted profitably, and undercut within minutes of being undercut. They all reduce the price very minimally when undercutting, and the "competition" isn't about price, it's about who can relist more frequently.
Congratulations on reaching Level 120! There are a myriad of new things to do. The first thing you should do is head to your faction hub ship where you have been doing your mission table quests and footholds to pick up and complete the quests necessary to unlock World Quests. World Quests will provide you an opportunity to grind reputation levels, acquire gear, and gather Azerite. There are tons of new things to do that we will cover in our Level 120 Battle Guide found here: Level 120 Battle Guide