3) What are some symbols and icons of this deity?
Sadly, any symbols of Hel were lost in the Great Christian Conversion. Lore involving her and her symbols wasn’t preserved, so historically we have nothing.
However, using UPG with my own work, skulls are a symbol she will accept, but doesn’t prefer. The primary symbol I have for her is a flower, typically either those found on graves.
One particular flower native to Helheim that she has grown is called the Hel Orchid. It changed from black at the center to bright crimson at the tips. This her personal symbol to me, and an especial favorite of hers.
Butterflies are another symbol of hers. Probably because they are so connected with flowers, and they are a symbol of rebirth. Hel began her life as a giantess, born of Jotuns, but she became a Goddess.