definitely takes turns. There's no point in redoing everything over and over. Make set times to make changes or set days.
I would get a dropbox account. That would just take away some of the tedium of uploading. Definitely each new save name it incrementally, like MyGame1.cap, MyGame2.cap, MyGame3.cap, etc. But then you can work out of the dropbox folder, and when you save, it's already uploaded, and when he turns on his pc, it's already downloaded. there's no extra process
aside from that, c1 doesn't really have too many team friendly features, I'm afraid