I would say, start slow with one, record timing, then try 2 in parallel, record timings, figure out where your bottle necks are. That’s how I started, it’s a lot of hands-on trying out for the first few days! As I said in another thread, don’t try to go too fast at first: GUI stop working in plotting - #3 by cultiv
You only have 1 plotting disk, so start with 1 plot (4 threads), record timings, then do 2 in parallel (4 threads), record timings, then your CPU might run out of cores, so maybe you can do 3 (4 threads) at the same time, with a bit of luck, not sure. But then you might need to start staggering them.