I'm not an expert on Crouton, but: 1) I haven't noticed any problems with battery or boot. 2) I use the cli-extra chroot, so no window manager. I have a tab open in ChromeOS with the crosh shell and switch back and forth to that. 3) None, so far. Before Crouton, I used the Secure Shell extension to ssh into a remote Ubuntu box, which was fine. Crouton makes it possible to have an offline development box.