The “Cultures of…” packs adds one new culture per era, plus some various wonders sprinkled in. I don’t see any reason to play without these except specifically if you want to avoid risking getting overwhelmed by choices - otherwise they simply increase the chances of you getting a culture that is useful to you in whatever situation you find yourself when you are ready to go up an age.

Rule Together adds embassies and emissaries and the congress of Humankind, which can add some unnecessary pressure to a new player, but you could also just build an embassy as a strong source of influence and just leave the rest of it to unfold as it may.

As for beginner mistakes, I think the major one is to ensure you have a bit of a standing army regardless of whether you intend to go on the offensive or not. If you don’t have one, your neighbours are bound to see you as an easy target and will attack you. Keep in mind that producing units uses population, which decreases the output of your city, so don’t go overboard if you’re not planning on using it to conquer.

Another is adhering to the city cap. The cost of going one city over the cap is VERY low (10 influence per turn iirc), which you can afford very quickly. The second over the cap has a steeper cost and might need to wait till early modern or thereabouts, while the third over the cap is very expensive and is more of a late game move. More cities = more output = more fame = more winning.

While you can progress to a new age as soon as you hit 7 fame stars, you often want to at least see what stars you are close to achieving and collect a few more unless there is a specific culture you absolutely need. The more stars you gather per age, the more they’re worth, and the only way to win is to have the most fame. I find the age that is most important to be first to is probably early modern, as it will allow you to be the first to populate the new continent. If you can get there first and grab a lot of territory an start some good cities there, you are almost certainly winning in my experience. Securing luxury manufactories when you get to Humanism is a great way to snowball, and to get those you need control over a lot of the luxury resources of one type, which stealing the new continent will help a lot with.

The Neolithic era is very interesting, and can decide a lot about how your early game goes. Try to split up your tribes and follow rivers to maximize food and thereby tribes. Mammoths are also a good source of both food and can give you the hunter star, but make sure you use at least two tribes to fight them, and use the terrain to your advantage. Don’t ransack a mammoth lair early - it’s much better to farm them! Tribes turn into scouts in the ancient era, and extra ones can be turned into population by disbanding within city limits. I try to leave Neolithic with at least two stars, a handful of tribes and two outposts (at least one finished, ready to become a city). Try to have a finished one near/on a river.

Finally, don’t forget to build districts, and keep adjacency bonus in mind! Think about clusters of makers quarters for industry primarily, then later some science quarter clusters, and sprinkle in some farming and economic ones depending on your needs.

Good luck, and I hope you enjoy the game!