Hiya!
See? THIS! THIS is why I prefer "old skool" mentality/mindset to the newer "want something new...go buy a book" and 'stick to RAW/official'.
I would belly up to your table any day of the week! Your campaign rules/adds sound like a lot of fun and have some nice flavour already. I can only imagine the interesting Campaign World stuff you have going on!
My 1e house rules are 'simple' overall. However, for the biggest changes/additions, I'd have to turn to my home brewed world of Eisla. If I was to copy/paste...well...that would be HUGE for a post (re: it's about 29 pages worth in PDF form).
Suffice it to say, after attempting some "broad strokes" to post here... I gave up. Too much stuff!
Most glaring: it is
EXTREMELY low powered. Highest level NPC in the 'world' (area about 1600km x 1600km; 1k x 1k miles) is 7th level! Almost nobody has a "Class". PC's start with 'bonus' HP's equal to their Secondary Skill category (either Sedentary, Average, or Labourer). If you are 1st level, you are better than 99% of the population. If you get to 3rd or 4th? Pffft! Fugettaboudit! You are top of the food chain, so to speak.
Magic Items are either very 'weak' (Potion of Healing, Amulet that can cast Light once a day, etc), or very 'powerful' (Sword of Sharpness, Tome of Persuasion, Chainmail +3, etc). And yes, there is an in-game campaign setting reason.
Monsters are rare, so to say. They keep to the dark ruins and deep dungeons and caves of the world. They avoid sunlight if at all possible. So much so that the majority of people in the world don't believe any of the "really big, nasty ones!" exist anymore (re: ogres, giants, manticore, dragons, etc). Orcs, goblins, kobolds, etc... "Yeah, I suppose SOME might still be around. But they stay in their caves and dungeons...like respectable monster should! Besides, even IF an Ogre actually existed still...the Gods would protect us, just like they did Pre-Cataclysm. So don't worry so much!".
Proficiencies are rolled using 3d6, with modifier dice for Easy (-1d4 to your roll), or Hard (+1d4). There are Critical Success and Critical Failure for Proficiency checks too (extra bad/dangerous result, or the opposite).
Quality Level is an Equipment thing. I call it the "CPAGMEL" system. I created it back around 2000, 2001 for my homebrew game system (not based on 1e, btw). It stands for "Crap/Poor/Average/Good/Masterwork/Exquisite/Legendary". These QL's correspond to penalties or bonuses. It allows me to easily emulate "environmental effects on equipment". For example, if PC's are wandering around a saltwater bog for a day or two, and don't have the skill, knowledge, background or tools to maintain stuff, I might have everyone reduce their "boots/shoes" by 1 QL. It gives the Players a better sense of 'reality' for their PC's...and gives actual mechanical reasons to go shopping for some new boots after getting back to town!
Oh, MU's are special. They have "The Taint", which is a magical mutational thing imprinted on their very soul! Basically, a MU is always recognized as an "Arcanist" (re: MU/Illusionist) by any living thing. Arcanists also have a visible mutation that they can not 'hide' for more than a few seconds, if that. It can be 'simple', like having pure white everything...skin, eyes, hair, and even blood! Or it can be more pronounced...just think 'extreme looking' (like a Tiefling/Alu-Demon, Dragonborn/Lizardman, or Azer, for example). Each Arcanist also has a "magical tell". Something in their spells (all fof them) that make them recognizable for who they are; example, a MU in the campaign is 3rd level right now iirc...pretty powerful indeed!...and he has 'chrom skin and solid blue eyes'. All his spells have the "theme" of mercury; sloshy sounds, chrome look, metallic smell, etc. His Magic Missile is a large barage of chrome needles with a slight blue glow that trail dissipating droplets of 'mercury'. Needless to say, people are pretty freaked out around Arcanists, so there are social advantages and disadvantages. Re: An Arcanist could walk around a bar, grab a bottle of whisky, and walk out....and nobody would do a dang thing about it.
Clerics have "The Aura". Much the same, but is specific to their deity and personality. They can't hide either; people will just recognize them as a "true" holy man/woman! One who is capable of performing miracles! (re: casting spells or turning undead...not that people think undead actually exist, but you get the point). The higher the level of Cleric, the more of his/her deities "traits" they start to show/develop (example: a Cleric of Thor might grow the most epic of beards and flowing locks...and project a feeling of being in a thunderstorm, perhaps even having little 'trickles' of electricity visible in his eyes when angered, etc).
There's a LOT more, but just no space here.

Twenty Nine Pages, remember? And that's not even the booklet on the world stuff!
^_^
Paul L. Ming