Running the FC up to shock level before stirring up the algae is not so much to kill it first but to provide a killing environment when you do expose the algae. I 'spose there's no real diference but I try to be accurate (when I'm not mis-typing).
Run the filter 24x7. No real need to run your SWCG. You'll be manually chlorinating until you're done with the shock process. Definitely don't run the SWCG when trying to determine overnight FC loss - you wouldn't want lose 4ppm FC while adding 3.5ppm via SWCG and think you're done when you're not even close.