Wow, so hard to translate "Ittekimasu"
What do you guys say to your family when leaving the house? I don't think there's a set of words to say in the western culture...

And can(do) female friends call each other "guys"?

Maybe something like "I'm heading out!" for ittekimasu?

And as far as females calling each other "guys', yes! At least in my experience, it's pretty common. I use it as a fairly unisex term, just like I do with dude and bro, haha.