Start with the end in mind - Stephen Covey
Pick a single project and get planning and working on it. Think with the end in mind. Write a pretend review from a journalist of your choice. What would the review say two or three months after it has been released?
Get familiar with everything at once to see what they share in common
In order to immerse yourself quickly and get familiar with what matters in those fields, find authors and podcasters that tie some of your themes together. Spend the time listening and find out what is current and what is important. Listening to these in parallel and at random times will let you see the connections between them. It inspires and gives you ideas about things you can drill into more thoroughly.
I listen to a few podcasters and listen to audio books that discuss programming, marketing and design. Most specialize in one area but there is quite a bit of overlap as you point out.
Learn just enough to get started
After a couple of weeks or so of listening you should have a more specific idea of what you like. Go out and pick the best beginner books in the areas that interest you most. Start learning just enough of what you need to get your project going. I emphasize beginner's books. You just need to get started
Committing to shipping continuously inspires real learning
As your start to build put your stuff out where it matters. Share it on social, post it on git hub. Find a place to display what you've got so fare. Ready or not. Any criticism you get is a gift in disguise because in one way or another people are offering ideas on how to make it better. As you build in one area, say your end product, you'll also think of things related to marketing and getting the buzz going about your project. The more you commit to getting it released you'll notice gaps in your project that need to get patched. This is a continuous cycle that only comes from committing to a shipping date and having an end goal in mind.