Draft of variant rules for a new campaign

For an upcoming campaign focused on hunting monsters, I started putting together a list of variant or house rules I’d like to use. Some of these are “official variants” directly from the books; others come from friends; and others are things I just wanted to include. The current version of this list looks like the below; I’d appreciate your thoughts and suggestions.

Action options:  The options Climb onto a Bigger Creature, Overrun, Shove Aside, and Tumble are available from the DMG.

Advantage: Players who do not have Inspiration (see below) can choose to roll with an extra d20 anyway, but at the cost of granting the DM a use of advantage for a monster/NPC. Note that advantage gained in this way does not allow for the use of the Rogue’s Sneak Attack feature or similar abilities; it only provides the extra d20.

Diagonals: When playing on a grid, every other diagonal counts double movement to approximate reality.

Elemental Damage: At the time a spellcaster receives a new spell that deals Acid, Cold, Fire, Lightning, or Thunder damage, they may choose instead to learn a version of the spell that deals one of those other types of damage. Exceptions exist where this doesn’t fit the rest of the spell effects (e.g. Thunderwave) or where the spell is specifically learned from a fixed source like a scroll or spellbook, so check with the DM in advance.

Equipment sizes: Mundane armor and clothing found in the world may not fit. (This rule does not apply to magical items.) The scavenger must roll a 1d6; on a 1, it fits perfectly. Otherwise, the equipment requires the services of an armorsmith or tailor to adjust. The cost will be the die roll times 10% of the normal value of the item. For example, rolling a 3 means that getting the item adjusted to fit will cost 30% of the sale price of the item.

Exhaustion: Every time a character becomes unconscious due to being reduced to 0 hit points, they accumulate a level of exhaustion. Each long rest removes one level of exhaustion, and downtime expenditure may accelerate that process. Note that six levels of exhaustion results in death.

Healing Potions: Drinking a healing potion (same character) only takes a bonus action. Administering a potion to another character still requires a full action.

Hitting cover: Attacks that do not hit a target may hit the object or creature providing cover. This specifically means that firing into melee can be more dangerous than you might expect from other games!

Injuries: Lingering injuries may occur when characters take extreme damage, such as failing death saving throws by 5 or more, or taking more than half of their max HP in damage from a single attack. These will not have direct mechanical effects, but will instead be used as Flaws, so that characters that effectively roleplay the injury get inspiration when doing so (see below).

Magic Missile: Characters who cast magic missile should roll 1d4+1 and multiply by the appropriate number of missiles for the level at which the spell is cast.

Multiclassing: Characters can take levels in additional classes if they meet the requirements in the PHB. The character should have already started to reflect the new class in their roleplay. For example, a fighter who wants to take a level of paladin may have already demonstrated their interest in the divine mysteries of the saints.

Padded armor: All characters are considered proficient in padded armor even if they are not proficient in light armor.

Sleeping in armor: For every long rest taken while sleeping in medium or heavy armor, the character accumulates one level of exhaustion. Long rests of that sort do not clear any existing levels of exhaustion.

Slow natural healing: At the end of a long rest, characters recover all of their hit dice but not hit points. They must spend hit dice to heal naturally, which will then affect how many hit dice remain for short rests during the day.

Spellcasting: Perceiving a caster at work requires the caster to be using a verbal, somatic, or material component. Subtle and innate spellcasting cannot be perceived. Identifying a specific spell while it is being cast requires a reaction or a full action, depending on the timing. For clarity, this means a caster must decide whether to cast counterspell on another caster without making that identification themselves. Other characters can try to identify it first using that reaction and communicate that result to a potential “counterspeller,” however.