Unfortunately you can't buy your way into gear that will make you ready for kara/heroics. You can get some decent buys tho, and if you have engineering or blacksmithing leveled it is easier as well.
However I would recommend chasing down the quest rewards as well. In the sticky there is a lot of drops, sure, but there are a lot of quest reward items too that combined with bought stuff should get you across the gear pre-reqs for raiding.
Warrior tanks are probably one of the more gear dependant classes, and you can't buy all epics for yourself (unless of course you get good rep with everyone and then you almost could). Get some decent blues, 1 or 2 epics and the occasional green if you are lazy, and then start raiding or doing heroics once you can. That is where you will get your epics, not from buying (unfortunately).
However make sure you get your hands on Gyro-Balanced Khorium Destroyer as you won't upgrade that in a long time. Cards are worth it if you have the money, but focus on reaching 490 def and the appropriate avoidance and armour first.