Originally Posted by Raetha

Most of those questions are answered in other threads, such as the DK tanking thread that seems to be more for new tanks. But I'll answer your questions with pretty much one word: Yes.

To elaborate:

Yes it will affect you, but your problem lies in your gear. Running heroics daily will help you gear up, as you get items not only from drops but from the emblems.

Yes, the titansteel is better than your saronite. You said something about your health/stam. Titansteel has a lot more on it, along with a slot for Austere Earthsiege diamond and a stam gem.

Yes, you are overcapped on def so the loss of def (so long as you don't lower yourself below cap) is worth it. Even if it does lower you below the cap, getting rings/better items will help you with that.

The only ideas I can come up with are to get BoE epics, whether they are craftables or vendor or drops from bosses. As it stands, Bracers of Dalaran's Parapets are likely to be very cheap lately. The titansteel helm will be better for you too.

In a nutshell, there are a number of tanking threads in the forum besides this one. Many contain upgrade information, ideas for tanking, and other good notes. If you read through them I'm sure you will find the answer to many of your questions.