Nice to see another Z34 being kept alive. If you’re new to working on cars, I’d focus on getting a solid maintenance baseline before changing anything: fluids, belts, hoses, grounds, and any old or brittle wiring/connectors.
Since you’re already into the brakes, I’d check the rubber hoses and hard lines closely too. And if you don’t know when the timing belt was last done on the 3.4 DOHC, that’s definitely something I’d put on the list. Take plenty of photos before unplugging things and tackle one issue at a time. Makes troubleshooting a lot less painful.