A substantial amount of reading? No.
A substantial amount of thinking? Yes.

do you think that in order to write a good entry book, which is philosophical in nature, that one would have to have done a substantial amount of reading first? — Aidan buk

Entry to what?

Writing anything down will make clear to you if there are areas you don't understand well enough. So the exercise is beneficial anyway. Good luck!

LOL I remembered when I took my first philosophy class at the age of 18 in grade 12-I was like, well its a social science class and I love and am great at political science, social justice theory, history, sociology, and english, sure I'll be good at this too, and then I left class the first day absolutely and irrevocably in love. Philosophy was all of my favourite subjects and more! It was thinking about thinking! It was knowledge for its own sake! Something i had been struggling with beneath the surface in those other subjects for a long time, which is probably why, almost three years later, I can no longer really find the interest in those subjects-the tests and questions seem pointless and repetitive, while philosophy is quite a good blend of creative thinking, art, factual reasoning and knowledge, and purpose. I remember not too long after that first discovery, I went through some of my writing from early middle school, so I was probably ten or eleven, and I found I had a whole journal of notes on how 'time is made up' and 'words aren't real, we just made them up' and I realized, shit, I've been doing philosophy all my life. I just didn't have the terminology such as social construction or intersubjectivity ect. that I have today. The ideas, and abstract thinking patterns were all there-I just needed the structure of a class to unlock it.

Philosophy is so hard to learn though, because there is no real building blocks-I mean, in math you learn numbers, then addition/subtraction ect. but in philosophy, you kind of start in the middle with (maybe) the key and most predominant thinkers, but the problem is a lot of those thinkers were influenced by more complex, less mainstream thinkers, which can lead to a diversion of theories and big words pretty quickly that might not make a lot of sense to the beginner.

What I would say is, keep researching and studying. If this subject really does interest you enough to write a book, then nothing should be preventing you from continuing to keep researching and studying. When I'm hooked on a topic/thinker/subject I spend most of my free time googling, reading articles ect. I'm sure lots of people on this site would be happy to direct you towards academic paper databases, such as PhilPapers.
Also, remember the golden rule depending on whatever kind of writing you are doing if you want to write well, you must read even better/more I am, and always have been, a ferocious reader, which means that writing comes a bit more naturally to me. Though, when I don't read for a long time, say when I'm in school, I find it harder to write so I have to force myself to read, even if its just more easier to read fiction, just to 'unglue' my brain. Reading = writing. So KEEP reading. But also, don't be afraid to start writing.
Lastly, the more information you have, the better you understand concepts, the easier and less painful writing will be. Don't get me wrong, writing is painful, but it is a lot less so when you really know what you want to write and know exactly what you are going to say. This comes with ample research. The hardest papers I have written are the ones where I didn't really know what I was doing ie. I didn't read the book or do much research, so I found myself sweating and trying to bullshit it all. Which comes out meh for the most part, and sometimes, as my grades reflected, quite badly. Don't do that. The more you know the more easier and clear your writing will be.

I'm just curious-what kind of philosophical book are you aiming to write? If you are planning on writing a more non-fiction, opinion piece, then you will have to do an ample amount of research to back your claims, define and clarify terminology, ect. If you are writing a novel with philosophical themes, then go for it! Though the more you know about these philosophical themes, the easier it will be to convey and to convey them correctly. Don't just read a wikipedia page and try to stick that idea into your book, it will come out very forced. A lot of the best philosophy, arguably, has been written in novel/fictional form, so don't get too paranoid, I think it will be fine.

PS. While Camus' works (novels) may be more readable to a mainstream/non-philosophical audience, by no means would I consider Camus 'surface level' if there can be such a term in philosophy. Camus ideas, especially as espoused in The Myth of Sisyphus and The Rebel are a lot more complex than they appear. I am saying this, not to be a snob, but because Camus is probably one of my utmost favourite philosophers. If you want to think about entry level philosophy-look on YouTube, there are a lot of useful 'crash course' videos there that define basic terminology and highlight key thinkers.