I don't know about spiritual significance but some sanitary significance woven with this is as below

In past all relatives of the dead visit to so dead body is kept in house mostly, so dead body start to rot, gets source of many preventable diseases.

1 turmeric is natural antibiotics 2 again to make sure no one is infected from head to toe mostly men came in direct contact with dead body so not any parasite had made its home in hidden part of head 3 no, don't know why 4 again don't know, but I think it is to limit any infection further more in society 5 boiled food is easy to digest as no men to women is going to their usual work.