Smith's ruminations on God's power and knowledge on pp. 69-76 are so irritatingly crude that there isn't much to work with here.
But Ok. God indeed cannot make square circles, cause an acorn to grow into a theologian, or turn Lot's wife into a pillar of salt.
What God can do is create nature itself which would then work according to the laws imparted into it. God could have supplied us with theologians by having them naturally grow from acorns; but He did not do so. Having created acorns that grow into oak trees instead, God must now heed the nature He Himself created and let acorns develop normally.
Again, it's impossible to "turn" a woman into a pillar of salt; God can only miraculously destroy the woman and create a pillar of salt with no continuity between the two.
Smith argues that "every indication of design in the cosmos is so much evidence against the omnipotence of the designer." (71) The reason is that an omnipotent God would not need to adapt means to ends, for such an adaptation is "a limitation of power"; every end would be instantly satisfiable, and every means would serve every end.
The answer to that of course is that God created laws of nature and the means-ends nexuses for our sake. We need these things. God does not. Moreover, while we need natural laws for our happiness, God does not need the universe as a whole for His own, because God is already perfectly happy. God did not create the world to satisfy any unfulfilled desire; rather, the world was the product of the self-diffusion of the divine goodness -- a unique mode of causation, neither physical nor teleological, that belongs only to God.