You can use M kernel with C-rom. And yes, flash it after rom and gapps. Personally, I flashed rom and gapps, rebooted, set up N7, then rebooted to recovery to flash kernel. It may not matter, just my preference. Enjoy!
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?