One of the wow gold guides I found on the net suggested having as many trade skills near max as possible between your alts.

With a team, we can basically have just about all the trade skills we care about online at once.

The general principle is purchasing materials, at a cost but in relative bulk, is more profit per hour then farming the materials and making much more per piece but less per hour.

Take a look at each of your professions. See what the common materials necessary for recipes are. Get a feel for average prices for these mats.

Then turn around and look at the average price for what you can produce.
A lot of things won't be profitable, but some will and others will be marginal.

Decide on what price you can buy mats, which would allow you to list items at a profit.
Anytime you see these mats at or below your target price, just buy them and produce whatever.
In general the mats are worth more then having 10x something in the bank.

Use Appraiser to list no more then 1-2 of a crafted item at once.
You can restock your mule periodically, and just Batch Post with them.
And know they won't list more then what you have set.

When a resource gatherer lists something on the AH, they lose the list fee if the item doesn't sell.
And, not everything sells the first or second time.
In addition, they lose 5% of the sale price, even for something like enchanting mats.
Selling directly to a buyer cuts out the 5% loss and the listing fees.

You can send an in-game mail to any seller who bulk lists your mats.
Offer to buy from them for "x" price, which is low enough to be profitable for you.
Some will take a sure thing bulk sale, as much as they can farm, over the randomness of the AH.

You can also create a few macro's, where you advertise something like:
/trade Buying stacks of <material> for <price>, CoD to <toon>.
If you want, advertise different mats by different toons, so the resources go to the right toon.

In effect, you are setting up the equivalent of a production line.