The normal thorium armor plans you get from world drop are crap. I'm a 300 armorsmith and i have quite a few of the plans.
You can get a belt and gloves plans from argent dawn that are alright but not worth it imo. The enchanted thorium plate items you get from the armorsmithing plans are usually on the ah and you need to get the top half and the bottom half of each one, combine em, then take em to the library in DM north to get the plans. These are pretty good and you can make decent cash on em but they do take a lot of mats to make somewhere between 300-500g worth on my server. The Dark Iron Plate items you can make from the thorium brotherhood you get once you're honored with em. That isn't too hard but it helps if you have someone that can get kingsblood for ya.
I personally made most of my money from armorsmithing by getting Plans for the Whitesoul Helm and sellin em for 45g a pop. It seems that horde get it better off as an armorsmith b/c of the plans you can make for shamans.
If you're lucky enough to get the plans for Stronghold Gauntlets or the Lionheart Helm you'll be set.