God needs man, or man needs God?
Of course man needs God. Allah Almighty created us to only worship Him; see Noble Verses 51:56 and 67:72. He also created us weak; see Noble Verses 4:28, 30:54 and 35:15. We need Him; see Noble Verses 35:15 (again) and 47:38.
To Him belong the end and the beginning for everything He created; see Noble Verses 53:25 and 92:13.
To Him belong the glory and the power; see Noble Verses 4:139, 10:65, 35:10, 37:180 and 63:8.
Allah Almighty doesn't need anyone in this universe, but we all need Him; see Noble Verse 35:15.
The word "serve" in Noble Verse 51:56 is a mistranslation. It should be "worship". Ask any Arabic speaking Christian, the Arabic word "Ya-bu-doon" does not mean "serve". It means "Worship".