Every custom, every belief, every fashion, every turn of speech?

No, of course not. Why would anyone waste effort on infinite irrelevant details? But everything there is to know, I know.

I do believe that player should be able to gain a basic understanding of the cultures their characters come from. The question is how much information can they get, and process?

You give them an overview at the start with the information you guess might be relevant or interesting to them, and supplement it during the game as necessary.

Part of the fun of DMing for me is in homebrewing cultures…or, more accurately, homebrewing factions that have a culture.

Besides which, there are some fundamental flaws in your premises:

You assert that a counterpart culture is easier to understand than an original one. I 100% understand any culture I make up, definitionally. On the other hand, neither I nor anyone else at my table can say the same about any IRL culture. Even members of a given IRL culture can never fully understand the totality of it.

You also say

[if] you create fantasy ancestries from scratch, you need to convey all that information to the players.

And I don’t think that’s true. Players don’t need to know everything about a culture to interact with them. In many cases, the player characters are themselves unfamiliar with that culture, in which case any mystery, mistakes, miscommunications etc are valuable in-character roleplay. And when the PCs would be familiar with a relevant aspect of a given culture, you can simply tell them that detail, no need to loredump everything. (Eg “I beg for mercy” “Your character knows that The Southern Pirates are notorious for never taking prisoners, are you sure you want to try that?”)

The DM gave him an OP magic item to compensate for his crappy build

Your worn items just kind of morph into your body when you wildshape. You don’t have to strip naked to go from humanoid to animal, for instance.

Magic is rare in most settings.

RAW that wouldn’t do anything though.

If you don’t want to do a one-shot, I still recommend keeping it short. 3-5 sessions perhaps. Just to dip a toe in and even out the kinks, and be able to feel good that you completed something. Decide if you want to commit to a big sprawling campaign after the first little demo campaign.

For sure! And that scarcity of resources and failing supply chains is a GREAT setting for questing!

A couple thoughts occur:

• If you wanted to justify big cities in wildernesses, you could use the prevalence of monsters to do so. Say it’s just too dangerous to have small villages, and everyone has to spend the night in a walled town/city for their own safety.
• I’m pondering how magic could effect this, too. You might have a whole Town in this ecosystem replaced by just a single wizard, who’s willing to magic up complex tools or luxuries in exchange for an exorbitant payment from the peasants.
• A lot of fantasy settings are lowkey post-apocalyptic, inspired by the Dark Ages and/or The Black Death. You may encounter isolated Villages that are struggling to scrape by as their Town got wiped off the map, or isolated Cities crammed full of starving refugees that fled their Villages.

Could you elaborate? How do their healing systems work? What makes them good?

Do you have a system you like where healing is a good idea? I’m a 3.5 native so I’m kind of used to the philosophy of “the best healing is killing them before you take damage.” But I’m interested in systems design in general and if there’s a particularly good example of doing it better I’d love to learn about it.

I know y’all are talking about like, buying a wish spell, but y’all make it sound like the mom hired a magic gigolo XD

Now you’ve inspired me. I should make a character who’s 1 level in sorcerer, the rest in wizard, and the premise is that they set out to prove everyone wrong that they’re not just going to rely on their inborn talents and they’re ready to do the work!

Really? I actually think it’s one of the strengths of 5e. In 3.5 you just have negative hitpoints down to -10, and that doesn’t scale with level or anything so it’s barely relevant after the first few levels. And it’s nice to not be just DRT when you get downed in combat.

You slightly moved the goalposts there. The assertion is not “Everything is making a political statement” it’s “Everything is political.” Your ikea glass reflects your social class, the international relations between where you are and where it was made. It may have been made by an oppressed person in some third world shithole (or even sweden!) It may even be a political statement, like a designer somewhere made it curvy because he thinks people are more likely to buy something with a “feminine” silhouette.

“Selectively simulationist” is a great way to put it. I think everyone falls victim to that from time to time and I’m definitely stealing your turn of phrase.

Wow, they really don’t let you have fun in 5e do they?

My current game might be helpful, but it will require a little context to explain and work to adapt to your purposes.

All my games take place in the same world. The last game was a pirate campaign, and, by the end, the players were legendary pirate kings (queens, nonbinary monarchs) that ruled the seas.

That leads to the setup for my current game: Sea travel is impractical and dangerous. A land route to totally-not-asia would be great, but none is currently known, due to a thought-to-be-impassible mountain range between there and here. The Explorers Guild is offering bounties on both a pass through the mountains and a viable charted land route to totally-not-asia. The players (and their rivals!) take a dangerous sailing journey around the mountains, to explore the jungle on the back side of the range and try to find a pass from that angle.

EDIT: They’re incentivized to work with the locals, because pissing them off would make a potential trade route dangerous and therefore worthless.

There are some formats where inventory management becomes interesting again. We tried doing a Hexcrawl earlier this year and there was a lot of interesting gameplay to be had in the risk/reward management of how many supplies they wanted to carry vs how much they wanted to invest in pack animals, limiting their ability to carry loot back, carrying this vs that, guessing how much they’ll use before they can resupply or where future resupplies might be, gambling on whether to press forward and risk running out or turn back, that kind of thing. It’s just the more currently popular adventure structures right now (eg linear or branching narratives) where inventory tracking is superfluous.