Can’t speak to it on the Fuji but on my Canon I tried using a monopod and found it caused more problems for me than it solved. Before you buy/take one or a tripod I’d also check the rules of the track to make sure they’re allowed, some venues don’t allow “professional” equipment.
For action sports I generally hand hold in shutter priority and do okay. Finding a shutter speed that gives the right amount of motion blur for the speed of the subject is key. And if you’re panning at low shutter speed get ready for a lot of missed shots. The one keeper will be worth it though. I will go between about 1/250 and 1/60 for MotoGP bikes to get nice blurry backgrounds in panning shots, depending on where I am in relation to the track. If they’re coming straight at me (or going straight away) I’ll go much faster and not worry about motion blur.
If it’s sunny you won’t have any problems with exposure except possible super bright highlights on shiny bits blowing out. I tend to do -1/3 or -2/3 exposure compensation and keep an eye on the histogram.
Because it’s a racetrack the cars will be hitting the same spot every single lap, so manually focusing on a spot and catching them as they enter your focus trap will give the camera less to do.
I rented a much longer lens than I was used to and took it out and stood next to the freeway to practice panning and tracking faster-moving objects, which helped some. It’s going to be really hard to keep a fast-moving car in the frame at 400mm. Good luck!
Can’t wait to see photos! Which race are you going to?