You’d better love your subject. If you’re going to write a book about it, it’s going to take you at least a year of early mornings and late nights and carving out time from what you’d rather do than sit alone in a room and write.
There will be a lot of despair and a lot of wondering if it’s all worth it. It will be hard and it will be long and when you’ve written the manuscript you’ll re-write it and re-vise it again and again.
Then you will give it to an editor who will make ever more changes. You won’t like some of them, but they usually make the book better. And you’re still not done.
You’ve got to get the thing published. Then you have to promote it until you puke. And then you will live with what you’ve done for the rest of your life.
You’d better love your subject enough to do the work to write a great book. There are already too many crappy ones.