Quite a big file to grab π
I can't answer your questions specifically, but in general advice only. Simualtions are simply expensive. As far as best practices go you are on the right track. There is space to improve and the first thing would be to see if you can do the simulation without fillets on the cube (proxy setup) and use that as a driver for high poly setup. Try some margin and explore possibility of turning of self collisions. Additionally, using project setting tab to reduce the calculation if possible is always good idea.
Hope this helps