A couple things:
1) when did nagato or Madara show a bloodline limit such as lava, boil, or ice elements? And Madara using mokuton doesn't count since he had Hashirama DNA incorporated into his body. The rinnegan has been said to use all of the base elements, not elemental combinations.
2) Gai's punches count because the enhancements to the body created by opening the Gates falls under suspension of disbelief.
3) Gold has magnetic properties. It is a diamagnetic element. Which means that when it encounters a magnetic field, it creates a magnetic field that is opposite of the field encountered.
4) white haired Uzumaki are simply old Uzumaki. The different colors of haircut for the Senju can be attributed to different genes being activated from parents outside of the clan, or just recessive genes being paired over dominant genes.
5) your timeline is an unknown variable. We have no idea when the sage lived, only that it was far enough in the past to have him fall to legend. The emergence of 2 distinct clans from a common ancestor shows a timeline greater than just 1000 years.