Yea I’m thinking of keeping the oem head unit it’s the touchscreen one without navAre you keeping the OEM head unit? If so, which head unit do you have?
You need a fullrange signal from the head unit, honestly you're much better off with an aftermarket stereo.
What you decide to do about the head unit will determine the rest of the supplies needed. If you use an aftermarket head unit, you can just buy an amp kit that has your power, ground, and remote wires as well as RCA's fuse holder and fuse.
The amp you buy will need to be based on how much power you are looking for at whatever impedance your sub is. Generally speaking, getting an amp that puts out good power at 2 ohms and a dvc 4 ohm sub that can be wired to 2 ohms is a great combination.
If you don't use an aftermarket stereo, you may need a line output converter, and you may need to use Vagcom to get a fullrange signal from your head unit.