I’ve made some improvements (changed the code block in my post above) and also commented what I’ve done better. I’ve set it up now so that the first thing that happens with any AutoHotKeys keycommand in the script is that it checks if Cubase is open and brings it to the front if it is. If Cubase isn’t running it passes the key stroke through with no action - so that key commands in other programs will do what you expect if Cubase isn’t running.
I have got separate functions for “focus project window”, “focus (or open) the mixer” and "focus (or open) the key editor so that others can easily use those as part of other macros. Hope it’s useful. BTW, I’m in no way a proper coder so what I’ve done may not be very elegant… but it does seem to work fine.