1.) Does PM leverage SUP?
Yes. In SCCM environments the core feature Patch Manager brings to the table is a tested and ready to publish third party catalog. Patch Manager simply publishes these updates to the SUP, and then they are handled just like any other update in SCCM.
2.) Installing the PM on it's dedicated server - Are the PM binaries going to detect the CM2012 installation?
Not directly. You'll have the ability to publish any updates you've deemed needed in your environment. From here you'll build normal software deployments to handle the update process.
3.) Are there any changes made on the CM 2012 console once the PM is installed?
One note about this as it comes up from time to time. Make sure you have the SCCM console installed on the Patch Manager server prior to installing Patch Manager. During the installation of Patch Manager a detection is run to see if the SCCM console exists, and if so it will integrate the Patch Manager tools. Once integrated, you won't really need to access the Patch Manager MMC console as all of the tools are made available directly within the SCCM console. This integration will only be visible on the server hosting Patch Manager / SCCM Console.