FFT giving a huge magnitude of first frequency and pretty much zero after that
That's correct. It's simply a property of your signal: your signal has very small "wiggles" with a very large mean value. Your mean value is about 1 and your wiggles are around 0.01 we would expect the first frequency to be about 100 times larger then all the frequencies. 

The first frequency represents the DC component (at 0 Hz), it's simply the sum of the signal.