There’s a lot of folklore around cast iron, so be careful when taking advice on what to do. Please wash your pan even if people yell at you for doing it; it’s hygienic and won’t strip the pan unless you have soap with lye in it. If your soap does have lye, you’ll probably want some that doesn’t.
Also, don’t feel like you need to coddle it. It’s a big chunk of iron. It’ll be fine despite people insisting you need to follow their way or your pan will explode. It can get weirdly cult-like. If you mess up too badly, you’ll just need to strip the pan and put a new layer of seasoning on it, which isn’t that difficult.
That said, you’ll probably need to use more fat than you thought you’d need while cooking when you’re building up the seasoning. Eventually, things will stop sticking as much, though.
100%, but to add a caveat on buying used, I’ve heard some people use cast iron pans for melting lead. Depending on who you buy from, you might want to test it before cooking with it, although I’m not familiar with how to test it or how common lead melting is/was.