I think I have a good grasp of stuff necessary for this, but I always felt that it's a really niche business, even within the DYI/open-source community.
If you want to start doing anything, I found it's best to look at the popularity of the board. S3E Starter Kit is by far the best, since most of the people could afford it, and it's nicely support. Any other board: case by case basis.
However, I doubt many folks predicted the wild popularity of Arduino or Rpi either. All it takes is for some cool applications. The price point isn't a huge barrier these days.
I keep hoping some post-grad will come up with a great DUMMIES like guide that covers Hello World to signal processing.
It starts from the absolute beginning, and the tools and tutorials are web-based and integrated with each other:
The focus is from Hello World to personal computer, but I've built a DSP-based guitar pedal in the past, and signal processing is really fun - I'd love to create a parallel learning path from Hello World to DSP at some point.