The fact you are losing a quart of oil, suggests the engine already had preexisting damage (potentially caused by previous owner not addressing the subarus oil needs, common) that you as the owner have left go unchecked. Clutches wear, shifter bushings wear. A/C, that sucks. The radio was aftermarket. The belt is on a manual tensioner, its meant to start squealing and need you to tighten it, thankfully this procedure is documented in the owners guide (source: Have one). So basically. Your list of unexplained failures is essentially A/C, everything else is either a) a maintenance item, b) damage as a result of poor maintenance or c) not even the factory parts of the car failing.