Torque them down till they stop and nothing moves...
I know there are torque specs out there (you can use the ones for the generic Garrett T3/T04 turbos), but I find it very hard to get the head of a torque wrench into that space.
If you happened to be able to torque them properly, the fact that they are 13mm bolt heads implies that torque should in the range of 20 - 40 lb./ft.
Once you get the turbine housing off, you'll expose the turbine wheel.
Right under the turbine wheel, you have a "cover" of sorts - this is the turbine heat shield.
http://turbocharged.com/catalog/parts_list.html
It is part #18 labeled here as "wheel shroud."
If the turbo is leaking out out the turbine piston ring back there, you're going to find a lot of crust black stuff fall out when you "spin" that heat shield.
This turbine heat shield is normally held into place when the turbine housing is bolt back in.
Once the turbine housing is removed, this heat shield can move a little bit.
If no oil is leaking back there, it's going to be pretty clean and no black, crusty bits will fall out when you shake it.
Some tips...
When you remove the 6 bolts holding the turbine wheel to the center housing, the turbine housing will most likely get stuck.
Note that two of the bolts are lined up with the oil supply and drain flanges.
Alternate backing these two bolts out evenly, and this will help "push" the turbine housing off the center housing.
When removing the turbine housing, try to keep contact with the turbine wheel to a minimum.
You can double-check this by spinning the wheels as you slowly remove the housing.
Initially, you can tap the turbine housing with a hammer gently in a circle to help it come off.
The turbine housing will be stubborn sometimes, and you'll feel like you're going to snap the bolts doing this, but I have never broken anything no matter how badly stuck everything is.
When you put everything back, make sure these two bolts line up in the same position.
It is important that the oil supply and drain flanges are vertically up and down.
-Ted