Should I take on a single social platform - facebook, insta, twitter - should I focus on SEO for google or google PPC - should I post across the blogosphere. I know pretty much nothing, but would love to start writing, sharing, and building an online business for myself. From my research so far, it seems a lot of success has come from simply building a major following on twitter or instagram and then leveraging that for monetizing opportunities.
It depends on what you topic, audience, aims, strategy, style, etc.
David Berman is right when he advises you to go where your intended audience already is.
That said, I do think it's important to own some online property of your own in addition to renting space / visibility on social media platforms such as Facebook, Twitter, LinkedIn, or Instagram.
Even if you use those sites heavily, try to blend that with reference to a home page where you call the shots and are immune to changes from on high. Facebook and Google implement drastic changes from time to time, and you don't want to be at their mercy.
If your Twitter following, let's say, is also part of your email subscriber base and has been trained to visit a home page elsewhere, then you're less vulnerable and more versatile. This isn't just about minimizing risk, it's about having more control of your brand and marketing.
As technologies, policies, and fashions change with the wind, you want to be able to pivot with them. Try to keep 1 foot in social venues and 1 foot on a primary branded location.
If you've ever been to a farmer's market, you'll see people with this same strategy. Yes, they set up temporary booths on someone else's property; but they ideally entice customers back to their main brick-and-mortar store.