Goldieloxx I would like to answer the questions regarding feet by the door and nails as I am on the Chevra Kadisah and can therefore answer corretly these questions
When we prepare the Mais during a Tahara, we clean the finger/toe nails in order but do not cut them as they are part of the person and the mais must be burried ‘whole’. Therefore so as not to do the same with the living as the dead, we do not clean/prepare nails in order and we do not if possible do fingers/toes on the same day.
As for sleeping with feet to the door this is because the oron with the mais is placed with feet towards the door. Again, so as not to do the same with the living and dead, we do not sleep/lie in this position.
Moish01 only flush nails down the toilet if they are well,well wrapped. Always ensure that nails are collected and disposed of in the correct manner as it is said that if not, one who has not collected his nails and disposed of them correctly will have to travel the world collect them all before ‘t’chias hamaisim. I am not sure how this translates into our understanding of today but I can say that I heard this in a Chevra Kadisha Shiur and yes it is kabalah orientated.