Is there some key combination to put the display on a mac to sleep using a windows keyboard, or somewhere where I can change the default key combinations?
function-win-shift-f12 (if you have hotkeys turned off where function keys act as normal function keys) otherwise, win-shift-f12
You can utilise hot corners on mission control, indeed it's quite handy for putting monitor on sleep or show desktop.
Simply you can attribute a corner of your screen to put on sleeping your monitor (by mouse pointer though, not with your keyboard, If you are using mouse/trackpad)
To activate this on your mac:
preferences > mission control > hot corners
You will see four corners and many options for each corners.