Why waste time finding a vendor, finding a guild that crafts for each other, etc..?
Make your account a guild in itself!
1. Guild leader. This is the CEO, the ‘big daddy’, the ‘main’ who leads in development. The long term use of this character is to farm for good drops to hand out to all the other characters on your account, and to farm for gold. This character should be optimized to be a good leveler, and soloist. Joining a ‘leveling’ guild (i.e. a guild that actually runs each other’s low-level characters thru instances) is beneficial. My personal recommendation is a tank-type with engineering, to wield a gun; Mining is recommended as the secondary profession, to fuel the engineering cheaply. Once you are satisfied with the engineering level, switching to enchanting is beneficial for disenchanting redundant, and weak, quest reward.
Development: pick your favorite character type, since you’ll be playing this one the most, and a strong combination of professions, race, and class. Get this character up to level 20. Obviously find a good guide to help you through questing mainly.
2. Farming: Get the CEO outfitted with bags, convenient bank accounts, and get a good farming guide. Generally find an area that farming is not too taxing (little downtime), and the level of drops is about right for the character you’re farming for, or drops lucrative beast parts for sale on the auction house / vendors.
3. Planning your employee:
Plan your employees not for roleplaying effect, or to be a one-toon guild, but how they will be efficient at time usage. Pretty much that means some characters will be all gatherers, and some will be all crafters, with the mail being your best friend at keeping the crafters supplied. It also means that some of your characters will be type-cast as professionals, based on their racial benefits—e.g. Tauren herbalists, and Gnome Engineers.
For resource gathering, Mining/skinning and Herbalist/skinning are classic choices, and giving them to a hunter is classic as well. Alternatively, some kind of tank with a gun skill is appropriate. And alternately, tailoring can be used as a resource gathering skill, so tailoring/skinning is appropriate if you hunt humanoids.
For crafting, keep the craft skills similar if possible. E.g. put tailoring/enchanting on same character, blacksmith/enchanting, tailoring/leather-working. Alternatively, making all your crafters take enchanting means that you can disenchant those quest rewards, but also requires way more characters to develop and manage—the choice is yours.
4. “Hiring” your employees:
Generally, don’t start rolling a new employee until you’ve amassed a good progression of loot to twink them with—some level 4-8 items, and at least one level 10-12 item. These can include green label items, nice vendor goods that have been enchanted, etc… The reason for waiting is that the leveling process to 12, will be much smoother and cost you less personal time.
Also, roll your employees to level 12 in order of how lucrative they are. A skinner/herbalist will bring a lot of money in early, while a tailor/enchanter will be a money sink until they’re well developed around level 20. Obviously, your first two employees should be gatherers, such as a skinner/herbalist, and a skinner/miner.
5. Developing your employees:
Continuing their develop to professional requirements is a much. The first hurdle is level 20. The key to making it smooth, other than just following guides, is to farm for them in advance / buy bargains on the auction house, and then buff those items with armor kits, enchants. As your ‘guild’ grows, it will be easier supplying new employees with goods from your own craftsmen.
Continue having the CEO farm for profession costs for the employees, and avoid discarding / selling plain items until your ‘guild’ can regularly make better ones.
The CEO should bank items instead.