Additional exhaust vents needed for whole house fan
If the TOTAL attic venting (ridge, soffit, gable, turbines, vent cans, etc. combined) is more than the fan requires, you're fine.  If it's not enough, figure how much more you need to add to satisfy the fan, then balance that to provide 50-60% of the total attic ventilation as intake (soffits or low on the roof) and 40-50% as exhaust (gables or high on the roof).  When you run the house fan, it can pressurize the attic and exhaust out of all the vents, including the soffits.  Since you only run the fan a short time in the morning, before the attic heats up, there won't be any issue with air going out the soffits instead of in.  When you turn off the fan and the attic heats up, the airflow will return to normal - in the soffits and out the ridge and gables.

A whole house fan needs 1 ft^2 NFVA per 750 CFM.  A 36" whole house fan moving 7600 CFM from the house into the attic needs a total of 7600/750 = 10.13 ft^2 or about 1460 in^2 of net free vent area (NFVA) from the attic to the outside.  

1460*40% = 584, 1460*50% = 730, 1460*60% = 876.  Thus, you should aim to have 730 to 876 in^2 NFVA in your soffits and 584 to 730 in^2 for exhaust as high as practical.

FWIW, a combination of soffit &amp; ridge vent (or near the ridge) is better than soffit &amp; gables.  The gables don't remove the hot air from above them or as effectively from the center of the house.