First welcome to the site!
From your first post you don't have an AV yet (which is fine, it's a fan site not just for owners) but when you get an AV you can save yourself some time having to answer basic questions if you put your year and model AV info in your signature.
I believe you can get Bluetooth adapters to fit the AV at places like www.crutchfield.com they have great customer service and can help you get the right adapters and parts needed once you get a specific year and model AV. As mentioned above the black square on the rear bumper is a cover that an access point for the rod used to lower your spare tire. (that system needs periodic maintenance and lube to work properly.) When you get your AV you will probably need to spend time reading the owner's manual to become fully familiar with all the features of an AV.
