Six years ago, I was transitioning from classroom teacher to entrepreneur/small business owner. I wanted an audience, because I'd be promoting myself and my company as a speaker, author, and book publisher. I started with Twitter and built a large audience in a year (I now have over 90K followers). While I love Twitter and know it helps my business, if I could go back in time, I'd scrap that idea and begin with email.
Forget marketing "gurus" who say email is dead; they're wrong! Email is still the top online marketing tool for any business. Is a blog important? Sure. A nice website? Definitely. A social media presence? Yep. You can work on all of those while you build your email list, and you can start that in a day.
Get yourself a fantastic giveaway (a lead magnet), find a good email service, set up your autoresponder, and run some cheap Facebook ads, leading people to your giveaway and email capture page.
I built my list to 10,000 in a couple of years, and I still wasn't working very hard at it. Even 500 good leads can be huge for a product launch. Plus, if you nurture these people properly in your emails, they'll become your ambassadors. Let me know if you have any questions.