I like your style and the direction you are going. I think I, personally, would enjoy this game.
There is a balance between gritty realism and playability. Making rests take long slows the pace of the game, but had little other effect IMO. Making magic and healing rarer and less effective is a BIG thing.
I don't know if this would appeal to you, but off the top I would suggest:
- Make money scarce: I've seen too many games get ruined because of an excessive award of treasure.
- Make magic scarcer than money: Magic items should be unique and interesting, providing an edge but not overly powerful.
- Have few "adventurers": Most people should be commoners. A village "priest" should be a commoner with religion proficiency, not a 5th-level caster.
- Nerf healing: Make it only 1 HD per short rest, max 1/2 HD during a long rest for regaining HP. You gain 1/2 your max HD after your long rest.
- Nerf healing more: Cure spells heal d4s instead of d8s, and d4s become 1 point only.
- Make going to 0 HP HURT: You gain a level of exhaustion when you reach 0 HP.
- Make going to 0 HP REALLY HURT: You cannot regain HP while you have any levels of exhaustion.
- Double the XP needed to level. That will also slow down advancement.
- Better yet, use milestone leveling and just decide if an "episode" was sufficient to gain a level. You control the pacing.
- Make death scary: Remove Revivify.
- Become an accountant, and make your players become one, too: Track everything. Rations, water, spell components, grain for animals, everything!
There are more, but that should get you started.