When I wrote for TV we always had what was called the series bible. It contained every bit of information that had ever been revealed one way or another about all the characters, the setting, and anything else anybody could think of. If you wanted to write an episode in which Uncle Ned visits, you could see what had ever been said about him. He's bald, he's hard of hearing, he did time in prison.
Sure enough, if anything ever slipped through you'd soon hear about it from some eagle-eyed viewer who felt compelled to tell you that 98 episodes ago somebody mentioned that Uncle Ned never learned any languages, yet in the most recent story you had him exchange pleasantries with a neighbor in Spanish. This would always be revealed with great glee on the part of your faithful correspondent.
The same thing happens to novelists, especially those who write series. Maria Snyder, author of The Scene of Magic and many others, suggested this a while back in SciFiNow magazine:
"Keep a story bible! There are tons of details, characters, places and names in a multi-series and if you keep track of it right from the beginning you won't waste time flipping through manuscript pages looking for information. I use a notebook for each of my novels. In there I write all the characters' names, they get a page of details about their physical descriptions, background, etc. Alos, when writing a series, plantng in little clues for conflicts in future books helps."
You don't need to know all this information in advance. Probably you will start with some basics and then you can add each bit of information as you go along.
(for friendly guidance in writing your book from idea through to publication get my book, "Your Writing Coach," published by Nicholas Brealey and available from Amazon or your other favorite bookseller.)