I'm not running i3 (any more; went to bspwm and then my own) but I've always started with normal Ubuntu. For i3wm I seem to remember it was reasonably straightforward as long as you're fine with some of the tentacles of Gnome. That is, I'd still typically run the Gnome settings stuff, and run a bar that'd happily handle docking of nm-applet and the like. I think next time I might look to a distro with xfce or similar and strip down from that instead as a means to get a cleaner system without the pain of building up from scratch.