There’s not a lot that can be said. The general advise seems to be: start small, record your timings and adapt.
Start slow with one plot, 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 2 plotting disks, so start with 2 plots (4 threads each), record timings, then do 2 in parallel (4 threads each), record timings, then 3 in parallel (4 threads each), record timings, then 4 in parallel (4 threads each), record timings, then your CPU might run out of cores, so then you might need to start staggering them.