We naturally assume that a book of the Bible tells the events in order. I would say most do just that. But not always. Like the ending of 2 Samuel, for example.
The main idea is that the firstborn — especially a son — gets “dibs” on everything, like the inheritance, or at least the larger share of it. But there is more to the word than just the idea of “the first son to be born.”
You’re going to see this a lot in the book of Judges. Someone is chosen by the LORD to bring victory, and he does, but he also does some things that leave you thinking, “Was that okay for him to do that?” (Typically: no it wasn’t.) And the Bible may not say anything to let you know if it was good, bad or indifferent.
It’s a straightforward (pun!) metaphor for doing what is right and typically what God commanded.
I found 13 events that lasted 40 days or 40 years. In some cases, the two are plainly connected. There may be more.
It is where the Israelites wandered after leaving Exodus. Sometimes it is translated as “desert”; I think “wasteland” is a good sense also.
It is a skin disease, but it has significance beyond that, even to the New Testament.
A chapter in the Bible can cover anywhere from a single day to hundreds of years.
God speaks directly to Abraham to give him three promises. But more than for only one man, these promises are the basis of the Old and New Testaments. No big deal.