What should you do in terms of preparations and how long is the process? Six months? A year? More or less?
Be fair, it's a very specific question that few people are likely to have good answers to, even fewer of whom will be posting on this board. Hell, I work in publishing and I don't have a clue. There's got to be a book about it out there somewhere. It looks as if "research" is your answer.
Forget the book publishing aspect for a minute - and think about general points that apply to any business venture: 1) What specific experience do you have of book publishing? 2) What do you offer that would make you stand out from the competition? Are you cheaper? Do you add value in some other way? 3) What is the distribution mechanisms that you have? 4) How do you play to pay yourself and any staff for at least a year without income or very limited income?
And the most important question: 5) What is the current demand for your product (book publishing) and how will that demand change in the future? Seems to me the trend has been publishers and distributors steadily going out of business, unless (of course) you publish and/or distribute university textbooks.
^Or you don't limit yourself to paper publishing. The company I work for, for example, is doing well, in part because we publish educational materials (though we're K-12, not college), but also because of our digital products.
Well what kind of publishing company are you talking about, Ebooks or actual physical books, or both? Anybody can get books printed, all you need is money, distributing them is what takes the effort and planning. Obviously distributing things electronically is a lot easier than putting them on shelves. I have started a magazine publishing company, but not a book publishing company, and it took us 4 months from moving into the office to having our product on shelves. But that was 5 people working flat out day and night, with a solid plan. It's a pointless question really, you need to sit down and just work out a plan, that will tell you how long it is going to take.
This reminds me of a Seinfeld episode... (paraphrased) Jerry: "So what kind of job do you think you'd like to do?" George: "Well, how about a sports commentator, you know the guys on TV who talk about sports all the time. I think I could do that." Jerry: "OK... what kind of experience do you have in that area?" George: "I watch a lot of sports so I know a bit about it and you know me, I've always got a clever quip to say." Jerry: "Yeah, but, you know they usually give those jobs to retired professional sports players, you know--the guys who have actually been paid to play the games." George: "Oh yeah... Dammit." If you don't have any working experience in the publishing industry, starting your own firm is going to be a major uphill battle. Not to mention the fact that it's a dying industry. Traditional book publication is being reamed by electronic publishing. And believe me, you can't compete with the likes of Amazon. Now, if you might be interested in becoming an editor, someone who takes a rough draft of a book and proof reads it for content, mistakes, etc, that's something that is always needed.
To become an editor you have to work for a publishing house usually and you rarely come in as an editor unless you already were one somewhere else. It takes a while to become an editor and make a living at it.