Classes would be built with their core aspects in mind, short rest features and long rest features - idea being that regardless of your campaign balance between rests each class is impacted similarly but uniquely.
Each class would have at least three sub-classes - one expands on the core-unique aspect, one focuses on the short rest stuff and one on the long rest stuff. More can exist and be added, but those are the building basics.
Spending HD would be expanded, giving every class something to use them for other than "HD in short rests" including things to be done during action scenes and during rests. Many of these may be sub-class defined and tiered. This makes to a degree the burning of HD the long term consequences that dont get fully replaced after a long rest while HP are more the "fluff plot armor".
Long Rests recover HD equal to tier plus ConMod - min 1.
Certain combat effects might also "burn HD" as an effect of their damage. Failed death saves for instance.
Material components would be thematic and chosen by caster - priestess of luck might use comics or dice, uses bone shards and grave dirt, etc. Costly components replaced by a magic fuel that is a harvest able, workable, crafting definable resource just like gold, steel, etc.
Outdoors at night typically dim light.
Resurrections et al require pre-componrnts - costly ones - called soul catchers that the dead guy has to be wearing at time of death otherwise no rezz barring wish level stuff.
Baseline two light weapons fighting let's you spend bonus action when you hit to add the off-hand damage die to the attack - no roll needed and a reaction to add +2 to AC against an incoming melee attack (before roll.) Feats, styles etc expands that.
Warlocks get meta-magic but sorcs get invocations.