Yep, that's what I did on my Dell 11 (wolf) with Xubuntu and almost everything working out of the box.I just created a vanilla Xubuntu USB, turned on developer mode and made a bios patch (the Dell has a bug, other Chromebooks don't require it), and installed.
After installation, I had to run something like two scripts to get the trackpad and suspend working.
Battery life is not 10+ hours as it is with chromeOS, probably closer to 7/8.
Yes, you can. And Chrubuntu has great driver support for the c720 and other popular models, but I still ran into some bugs with suspend and Wifi, so I stick with a chroot.
Crouton is a install script that uses a chroot to install Ubuntu through the shell on ChromeOS. You still need to enable developer mode, and it uses the ChromeOS kernel, but other than that it looks and feels like a "normal" Ubuntu installation.