To me, this sounds like advertising. Advertising your books and yourself. Anything you want to sell in large amounts needs advertising.
You don't have to do large amounts of advertising to get a following, though. Facebook, Twitter, Google AdWords, and more all have inexpensive advertising. You can do as little or as much as you want/need. The thing about getting a following is that at a certain point (often called a tipping point), it'll take off on it's own and you won't have to manage it as much.
You also don't need to start at 1000% from the beginning. You can start a simple website at Wix, WordPress, or other website/blog creation site. Even having Facebook, Twitter, or similar social media page can help get you started. It really doesn't have to be complicated to begin with. These can be worked on nights and weekends, just adding content and design as you have time and energy. To help you get things moving, you can even draw out a basic idea of what you want to look like on paper (think napkin at a coffee shop on your lunch break), then work on designing it later. This is what us web developers often do (we just do it faster, because bosses and deadlines, not because we're necessarily better at it).
You might want to start out with a basic personal profile, like a Facebook page. A simple photo of you or whatever inspires you, a basic bio about you and what inspires you, a list of things you're proud of doing/writing, and some other background info as to why people should be interested in you. After you get a bit of a following going, you might even want to start your own Wikipedia page with all of this same info. If you get really popular, other people will start maintaining that page for you, for better or worse. If you already have a FB or Twitter, make a sub-page or account that's specifically for you as a writer. You can still link to your personal page, but keep them separate. Also, keep what you post on each separate and on topic. If your kids win a sports game, put it on your personal account, then maybe write about it in your genre on your business account, but don't use your business account to post all your "night out" selfies, unless you write "valley girl" books.
There's 3 things that I find that sells: cute, adorable, and relatable. Cute will get you some sales, but it's not reliable. Adorable will have physical items flying off your store shelves, but it probably doesn't work for writing and unless you're a Barbie girl, won't help your bio. (FYI, adorable is essentially cute plus emotional reaction to item.) So relatable is really what you're looking for in this case. You don't have to be a back-country-girl-next-door type to be relatable, you just need t o be relatable to your target audience.
If you write emo/goth books, be relatable to them. If you write romance novels, be relatable to housewives. If you write action novels, be relatable to testosterone fueled men. If you are relatable to housewives and write action movie style novels, you've missed your target. You don't have to be 100% relatable to everyone in that target audience, because that'll never happen, but try to start out that way.
Don't lie in your bio, but stay on topic at first. Once you get more of a following, you can add more that isn't on topic, which will make you more relatable. Write about yourself like you write in your normal writing. Don't make it into a resume, unless you're a business writer, but rather write it as an expression of yourself in the genre you write.
A platform may not be 100% necessary, but it definitely helps. As a reader, if I don't know a writer's name, I probably won't pick up the book. If I happen to find the cover artwork interesting, I'll look at the reviews to see if they are known by others as well as to see if they and the book are any good. When I see something like "I love Issac Asimov and this book is no exception." I know it's likely to be good as well as helping to keep Asimov in mind for other purchases. If I really like a book or a series of books from an author, I Google them, trying to find out what else they wrote. If I can't find anything, I'm probably not going to buy another book, since I don't know what other books they have. It's really that simple: if I can't find out what they've written, I can't buy more.
Advertising yourself might feel a bit boastful, self-righteous, bragging, or other negative descriptors, but as a writer, it's absolutely necessary. If you don't no one else is likely to do it. You can't be a wallflower and expect to sell anything, unless you have a publisher to do all this for you. Even if you do have a publisher, they will likely want you to have this for them. So yes, it'll likely help you get a publisher if they can already find you and don't have to push you so hard to get that going. If all they have to do is nudge you to update your content, it's 100,000x better for them than trying to force you to start from scratch. They know it takes time, including time away from your writing, so get started now, so you don't have to try to do it all later.