Will a factory reset launch to the android stock launcher or can I use my own?
Factory reset will wipe all user apps, thus if you installed Nova regularly (not as a system app), then it will be gone, and after the reset you will be greeted by the default launcher. If there isn't one and USB debugging is not enabled (very likely), you're stuck.

At this moment you should definitely install a launcher (Nova or whatever) as a system app to prevent the worst case.