God's self-sufficiency means that He does not need anything outside of Himself. He has no lack. But, His creating us does not mean He is insufficient. It means He decided to create us for a reason that was sufficient within Himself. Let me offer an idea. Perhaps the reason God made us is to fulfill the nature of love. The Bible says that God is love (1 John 4:8). It also says that love gives. John 3:16 says that God so loved the world that He gave His only begotten son. Finally, Jesus said in John 15:13 that the greatest act of love is to die for someone else. So, since God is love, love gives, and love means to die for another, perhaps God created us in order to provide an opportunity for Him to manifest the very nature of love. You see, by creating us and allowing the fall, there would then be an opportunity for God to give us His Son to die for us, thereby fulfilling the nature of what love truly is.