1)
2) Nova works great on the G4. The only downside I see is if you like LG's widgets like clock/weather, calendar or tasks which are baked into the default launcher and not available on 3rd party launchers. There are plenty of 3rd party widget alternatives though. I personally use Transparent Clock and Weather Widget, Google Calendar and Google Keep for tasks and reminders.
One other issue with 3rd party launchers like Nova is at the default level you lose the ability to double tap anywhere on the screen to turn it off. However, you can either double tap the status bar, or go with the solution I chose, which is install one of the various Screen Off apps out there then set that app as the double tap gesture in Nova Prime.