Once you have your finished product and have a price for it, keep in mind that using either your faction AH or the neutral AH also costs money: if the item does not sell, its deposit is taken by the AH; if it does sell, the deposit is returned, but a cut from the payment it taken by the AH as a commission. You must factor this into your selling price: your faction's AH will take 5% from your sale, while the neutral ones will take 15%. You can factor this into your cost to determine the minimum price at which you need to sell to at least break even:

A stable for any healer. While not every healer uses this, those that do swear by it. It allows you to set spell combinations so that every ability you use is at its optimal effect. Healers have a large range of buffs and healing abilities, and Healbot lets you use the best ones you need when you need to. It’s a great organizing tool for any healer.

The other addons are a great addition to the repertoire of the gold maker. Some add percentages and buying lists, while others provide price and revenue graphs to the reader. Chatter even allows you to repeat those WTS messages without sifting through pointless gossip and chatter. The in-depth workings of them will come later, as for now, more basic setup needs to be covered first.
A successful transmog goldmaker like Studen farms for three hours a day on most days. They're on a near perfect server for their market, with a large number of active players with a decent amount of interest in transmog. They have thousands of unique, high value items on the auction house at any given time. To top it off, they find great enjoyment in the grind. If you can find the time, and enjoyment in farming hundreds of items from low-level dungeons each and every day, you might just be the next Studen.
The amount of bots in this game is absurd. Constant flow of cheap herbs and other crafting reagents coming into the game and nothing is being done about it. I've noticed there is two big players working the auction house with their massive bot accumulations. These 2 big players appear in over 30% of the auction houses across all NA Servers. I've not checked in EU or other regions but I'm assuming they are also plagued. I've included some screenshots just so you can see how bad it is.
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.