Should I install a grounding rod near my light post to protect against lightning?
You can put a proper ground rod there if you really want to, and tie iti n with the grounding system.  There's no restriction on grounding, what you can't do is tie neutral to ground.  

Now... Why are you putting GFCI outlets all over the place, outdoors no less? GFCI devices perform very badly outdoors and it will be a maintenance headache.  

You only have one circuit, so you only need one GFCI device.  If this comes as a surprise to you, this is a great time to get educated. Save you a fortune in the long run.  

And put it indoors. So it's out of the weather.  

If you're simple, fit a GFCI breaker.   Otherwise you can run EMT conduit off the service panel to a nearby location (like right next to the panel) and fit a steel box,  and a cheaper GFCI deadface or liveface receptacle there. That will position it to take the lightning hit instead of your expensive stuff. 

The outdoor circuit gets fed off that, and you use plain receptacles throughout.  If the circuit has good grounds, you should be able to confirm the efficacy of the GFCI protection with a pocket tester.