As asked, I want to set up a dice pool for a variant of mine on the school of necromancy subclass for the wizard. How to do so? My vision is that this feature, "Harvest Life", gives the necromancer a pool of dice equal to their level, they can gain dice whenever they kill a creature with a spell, twice the amount of dice per creature killed when they use a necromancy spell to do kill things, and they can also spend a spell slot as a bonus action and get dice equal to the level of the spell slot. Also as a bonus action, they can heal themselves or others by spending a chosen amount of dice from the pool. Furthermore, the level 14 feature allows them to use all remaining dice to heal themselves as a reaction to dropping to 0 HP. The pool is also refilled after a long rest. How can I create such a feature? Its like how the sorcerer has a tracker tracking the amount of sorcery points they have.

That would be done with an Action and “Limited Uses.” (The uses represent the pool, the “damage” roll for the action represents the dice.) so you would create a parent class feature that has the “Necropool” (or whatever) Set up as an Action with limited uses and a “damage” roll. Then. All of the abilities that use the dice from that pool would get added as Actions attached to “Options” that are themselves attached to that parent feature. In that way, the uses will be attached to the pool and whenever the player taps/clicks the action they want to use, the pool of “dice” will be immediately available on the sidebar.