In addition of English and Sicilian, what else is required

In past, I and my friends did strongly prefer king pawn (e4) opening. My response has "always" been c5; with reasonable success.  For queen pawn (d4) opening, my typical response is d5.  Recently, I have replaced the e4 with English opening (c4).

To go from 1500 to 1700, is it enough to hone the English/Sicilian skills and to have reasonable d4 response?  What else is recommended?