The C is a neat ride - congrats.
I would absolutely investigate a coolant heater, particularly since the Prius hybrid functions are so temperature-dependent. You can get the thing to stop the engine much sooner in your drive with a bit of pre-warming. (More efficient to warm with grid power than gasoline, too.)
I'm not sure how developed the Prius C mods are yet, but there's also a coolant sensor hack for the liftback that enables you to enter engine-off mode sooner. Member Daox did one to his car - have a search for it.
Grille blocking is absolutely worth looking into (for the Florida "winter"
), but you'll want to closely monitor coolant temps with a ScanGauge or equivalent to ensure you don't over-do it.
Welcome to the forum!