How do I calculate peak amplitude of the signal components after zero padding and FFT?
It looks to me like your frequency resolution is sufficient and you are getting the correct value of the peak magnitude in your FFT but your scaling factor is incorrect. 

You are right in dividing the magnitude of your FFT peak by N (1024 in your case). This number however, divides the power across the positive and negative sides of the frequency spectrum. 

If you only want to look at one side of the FFT, you should multiply your peak magnitude by 2/N to get the correct amplitude that you are expecting. See this answer for another example.

e.g.

512 * 2 / 1024 = 1 (the answer that you were expecting)