What temp did you mash at? If you were toward the high side, 158F you would create lots of unfermentable sugars. If you keep your temps lower, 148-152F, you will make a more fermentable wort and your final gravity will be lower.
Creating a yeast starter is a good thing for liquid yeasts. For dry yeast, a starter is not needed. Rehydrating the yeast is a good idea. 4 packets is NOT too much for 10 gallons. I really don't think you can OVER pitch yeast. Under pitching is far more a common failing.
I am currently enjoying a pale ale which started at 1.050 and finished at 1.010. Mashed at 158F. 10 gallons of final product pitched with 4 packets of rehydrated S-05. VERY NICE!