Richard Westfall's Never At Rest seems to be the definitive version. I have the abridged Canto version entitled The Life of Isaac Newton, which has served me well, although I have consulted the original for its discussion of some mathematical details.
I also have James Gleick's ISAAC NEWTON, which is comparatively a breezy read, but not without merit, and I would certainly recommend it as a starting point.
Have you read up on Tesla too? He was unbelievable.
I wish he was alive today to see what he made happen- and just imagine what he could do with modern computers at his disposal.