You should be able to put your computer to sleep and then have the simulation pick up when the computer wakes up, but there is no pause button that allows you to stop it without the computer going to sleep, other than canceling it. It should only be using one processor (unless you are using PAT), so it shouldn't be hogging too many computer resources.
If you are doing preliminary runs to check things out you could consider partial year runs, and you may also want to investigate ways to speed up the simulation, often geometry complexity is the culprit, but there could be convergence problems.
Yes, you can do this from the operating system shell. Which operating system are you using?
I'm using windows 10.