I would not write the history. The history is background and setting; some of that will necessarily come out in the first ACT (about 25% of the story) and more can be revealed in the rest of the book as you go along.
You also don't need a complete history of your main character, or the other characters. You need enough so you feel like you know the MC and how they will behave or react in various situations. Their history shapes their personality, but readers don't care too much about the history, they care about the personality!
Beginning writers often like to tell the history to justify why a character is a certain way; but that is "telling", not "showing".It also isn't reliable; just because somebody grew up in a rough neighborhood doesn't automatically tell us his personality. Not every woman that has been abused or raped will show that in her personality. In fact she may not want to show that. Knowing their history is not how we get to know people in real life.
IRL we see them react to things, deal with problems and have confrontations, and by their behavior (and sometimes dialogue) we learn who they are. We know by their friends, and what they find funny or irritating. Later we might ask how they got that way, and hear their story, but that isn't always necessary, unless there is something very unusual about their personality; but IRL if somebody is always joking around, or is always serious, we don't need to know why they are that way, we just accept them as that way.
A detailed setting can be nice, lots of things for the reader to discover and be entertained by; but that is not what the story is about. The story is about people, usually just one or a handful, that encounter a big problem, so big they discover they cannot handle it like all the other problems in life, they have to put other things aside and dedicate themselves to this problem.
That is what you need to start writing. One or more MCs. In the first half of Act I (=10%-15% of the entire story), you introduce them and their normal world, what they are doing day-to-day, how they deal with minor life-problems, and to an extent by following them in their normal world, what the normal world consists of. At about the halfway point, there is an "inciting incident", something happens and they have to deal with it. Just like us dealing with a flat tire, they try to deal with it in the course of continuing to pursue their life in the normal world. But it doesn't work, the problem escalates. Until at the end of Act I, the MC(s) must leave their normal world, either literally or metaphorically, and devote themselves to actually dealing with this escalating problem.
A story is not about the setting, it is about people in the setting, following the rules and using the resources of the setting, to deal with some big problem.
In general, throughout a story, we always need the reader looking forward to "what happens next." In the next few pages, or at the end of this scene, or at the end of this chapter, or Act, or at the end of the book. Preferably all of those simultaneously!
The problem with reading an encyclopedia about a new setting is there is no tension of wondering what happens next. There is no action. The details may be interesting, but use them in your descriptions so the reader gets them along with the action, or in-between action scenes.
Start by imagining an MC (or a few), and imagining a life-changing problem they will have to face that is going to be outside their comfort zone and skill set; so it isn't going to be easy for them.