Ok I've got the stuff, now how exactly do I go about doing this?

I've also got a 180 tstat here and I am thinking it makes sense to put that in now... correct?

Just noticed you said that... yes it has...

Actually it would be silly for you to put the coolant in just yet. You need to figure out the leak... and can fill wil water to do so. Once you figure out where the leak is, drain the water out, pull and change your tstat while fixing the leak. Then fill back up with nice clean coolant.

YES!
I just replaced mine.
I would suggest looking there. It comes out of the tensioner pulley bracket, makes a 90 degree turn then goes into the lower intake manifold under the map sensor. The lower intake usually gets hot enough to make the coolant burn off so look for a film or stain underneath the plastic elbow on the LIM.
I found one at pepboys after some idiot at autozone tried to tell me it was a dealer only item.
5 bucks plus some RTV.

Yeah..it'* max a $15 part, but a PITA to put in.

re: throttle body gasket and temp gauge:

"Just noticed you said that... yes it has..."

Sounds like the throttle body gasket to me. An easy swap. Two beers.

I'd fix the well-know upper problem while you were in there. It'* gonna fail, it'* just a matter of when.