Horcrux thoughts
Might Walburga's portrait be one? Perhaps paintings in general? They are supposed to keep some part of the original person, so how does it differ from the horcrux process? Could a person in a painting become three dimensional again? If they can be horcruxes, they would be a great method to spy, particularly if you have a snake with a horcrux that can hide in paintings and listen in (further on the spy note, have as many paintings of yourself made as possible, hide one underground somewhere, and disillusion the rest and stick them everywhere)
Preparation for temporary death:
Get a body made, put draught of living death in it, possess it if discorporated
inhabit the body of someone recently given the dementors kiss (imagine Sirius not out-running them and Voldi being in the neighbourhood)
Dealing with horcruxes
Can you transfigure them into something else, thereby destroying the soul piece? Perhaps if you transfigure it into something the soul despises quite vehemently
Are there muggle means of destroying the items that holds the horcrux "beyond all repair"? Could you chuck it into the sun or throw a bomb on it?
What to do with your horcruxes/what items to use
1. use inconspicous items like bland rocks
2. hide them in places without any particular significance - put one on a satellite or other space-bound item that won't return to earth any time soon. Throw one into the ocean. Keep one in a rental storage unit. Keep one in your vault, one in a hole in the ground in the middle of nowhere, one in your lair.
3. Accept that you won't remember their location at some point. You plan to be immortal, you will forget where you kept your stuff.
Effects of horcruxes on their creators
Outside of making a person essentially unkillable, what do horcruxes actually do? They clearly don't ensure either mental or physical health. How many suprisingly old wixen are actually keeping a horcrux somewhere they can't remembet, locking them on earth forever, with steadily decreasing mental health and faculties.
Living horcruxes
What would happen if Harry met the gaze of the basilisk – would he die or the horcrux? Same for the dementors, the veil, and any other soul-sucking creatures or artifacts.
Misc
What if areas like the Bermuda triangle only have such bad reputations because loads of dark wixen stash their horcruxes there, forcing them to quibble for every minute without distraction in form of random people and boats to destroy