1. The general consensus is that there were more people. This is assumed in Genesis and it (annoyingly!) doesn't bother to explain it, as the audience at the time already assumed it. Also, the authors weren't interested in all the logistics and technicalities that we are today.
2. Cities referenced in Genesis were likely fortified settlements, rather than like modern cities.
The idea that people in Africa could only build simple huts is a myth that came from the colonial era. Africa had large cities, architecture and metallurgy while parts of Europe were still tribal.
If you're keen to learn more, there are some good books that explain this much better than a comment can, such as "How to Read the Bible for All Its Worth" by Fee & Stuart and "Genesis for Normal People" by Pete Enns. I haven't read it but "African Civilizations" by Graham Connah is probably the go-to book on how African cities and technologies were so much further ahead than traditional European/US narratives place them.
The best resource for these kinds of questions is probably "The Bible Project". They have a load of YouTube videos and podcasts that cover these kinds of questions.
For example. It is easier for a Camel to go into the eye of a needle than a rich man to get into Heaven. If you read this, it makes it sound like Abraham cannot get into Heaven, wasn't he wealthy? Heck, there's others who were wealthy in scripture, even kings are they all doomed? In Aramaic the same word that in Greek is said to mean camel, can also mean rope.
If you think about a rope going through the eye of a needle, and what it TAKES for a rope to go through the eye of a needle, aka removing all the threads or layers (humbling the person and forcing them to strip themselves down to their core) in order to make it through the eye of the needle. Or in other words, you must be willing to dethatch yourself from all your wealth. Remember the guy who asked Jesus was he must do to be saved and enter heaven, and walked away when Jesus told him to give away everything he owned to the poor? That is the same exact message.
There's a few other verses, but that's the main one that always strikes me. Some of them are far more nuanced and I get into hours of debate with people who are ignoring everything I am saying (I don't know why, I try to lay it all out in the most simple way possible) as if I'm breaking the law, but its obvious to me that we don't have perfect copies of the Bible. I still think the overall message is the same though, so nothing wrong with that. It proves yet again that men are all fallible.
Sorry for the tangent. I used to deep dive translations and their nuances, and the Aramaic based Bibles are very interesting.
There's also an Aleh Tav Old Testament Bible which is fascinating to me. It adds the Aleph Tav anywhere it would be in the Hebrew into the English.
This is a great question. In the next verses, the disciples ask pretty much the same thing: "Who then can be saved?" and then Jesus explains to them:
Whether it's a camel or a rope (and whether it's a literal needle or a small city gate, as some people argue), I think is less important (though still interesting). Either way, after the rich young ruler walks away, Jesus turns to his disciples and paints a picture something that's completely impossible without God, no matter how hard we might try by ourselves.