Here's what I did when I started a horde team (I mainly play ally) on my PVE server.

I transferred 100g through the neutral AH, bought lots of cheap netherweave cloth, and found a tailor willing to craft bags for me (50g gone, approximately), try to make sure all your slaves have maximum bag space.

Loot all the stuff that drops, and if your bags are full, prioritize in this order: White stuff, Grey stuff:Weapons, Plate, Mail, Leather, Cloth, Rubbish. But try to maximize the amount of bag space you have at all times. (get bigger bags)

Vendor every single grey item that you don't need or can't use to replace an armor item. (I like to have every tiny bit of advantage I get)

Some people like to level an enchanter to DE stuff, I vendor soulbound items for the money instead, because I'm too lazy to level enchanting. :P If I did, and couldn't gain more skill from DE'ing, I would enchant all the items I can before putting them at the AH, looses you some copper/silver in enchanting mats, but makes it more likely you'll sell the item., and you skill up your enchanting.

Check all your white stuff towards professions before vendoring (Maybe check the going rate at the AH), and sell it at the AH if it's worth the effort. (I consider trying to sell the item 3 times as a guideline to if I'm putting it up for auction or not)

Put all your green BOE's on the AH (The addon Auctioneer or something similar is great, also for the white things)

At level 20, I'm still at only 50g, but I've got all the trained spells, plus all my guys now have full sets of NW bags..