Yea what redog said to get the thing out. The HVAC knobs can kinda suck to unhook, but well work it to get everything out of the way.
Your gonna need one of
these or something similar.
As for a harness with the chime still active, I would go with something like
this or, if you have and amplified system, like the monsoon system, you will need
this.
If you give up on the chime go for
this guy.
Other than that, make sure you dremmel out that steel rod back there in the opening, so everything fits all nice and purdy-like. While your at cutting stuff, I had to cut the top right corner of the screw hole in the plastic spacer kit to make it sit flush. You may not have to, but I did.
Other than that, make sure you have a decent stranded-wire wire-stripper, preferably 16-24 gauge capable, or somewhere in that range, and a whole bunch of wire connectors, usually crimp-type.
Lastly, WELCOME and have fun!