I prefer the ISBoxer route due to wanting to see all of the character screens at once. But, system specs are very important when doing it this way for anything above 6 characters or so. So, depending on your system, will determine what you can and cannot do. I would say if you have a singular 4060 card with whatever RAM count, I think this is likely why you are crashing after a certain amount of instances. Allow for 2GB of system RAM per instance with 1GB of graphics memory for most graphics options maxed out with a background of 30FPS and foreground at 60FPS. Do the math from there. Now, of course, you can modify what graphics you use with whatever intensity in your options to account for how much memory you actually need.
Anyway, there it is...