Hello! My name is Humberto Valle, I'm the co-founder of www.Unthink.me, growth hacking and digital marketing service. I can go over all the different tactics and strategies that you can implement but there is a book by a fellow growth hack marketer, Ryan Holiday, in this book he talks about how he did just what you are looking for.
In essence, he scheduled his book release with enough time that allowed him to promote snippets of the book through blogs, forums, influencers, etc and get traction on this website to capture emails from interested marketers and business owners. You can also trade emails for snippets/sections of your book as well as schedule a timeline releasing chapter by chapter through a blog wrapping up the entire project with the release of the book itself. (sounds contradictory, but if your book is good people will want to have a physical copy and support you for it)
Once the book is launched you reach out to influencers who have shown support before hand as well as through emails and even paid ads. Check out his book is definitely worth it.

This will depend so much on your current audience and your genre. But all reviews are is making connections with people who are excited about your book.

Creating a mailing list helps you get people on board, and you can then ask for favours like for them to leave a review in exchange for a free copy of the book.

This will also depend on your goals in publishing (i.e. to get information out there, to publish a book you're passionate about, or to try to earn a living), but you get better with time, practice, and building an audience. Your first book might not get as much traction, but building upon that with subsequent releases will help grow your audience, and the number of reviewers you have on your team.