Hello,
As far as I know the scratch-blocks repo doesn't really provide developer docs, because they're not really focused on being a library :/
I think that for most intents and purposes pure Blockly is probably going to be the better choice. If you want your blocks to be in the style of scratch/pxt there is a new
zelos renderer that makes them look like that. If you want to use a few scratch-blocks specific fields, it's pretty easy to move them over. And I believe the toolbox refactor that is being worked on will eventually make it easier to have a scratch-blocks-like toolbox. But on that last point I'm not sure hehe.
If you don't want to use Blockly I think you should also look into the
pxt-blockly library before settling on scratch-blocks. From what I've heard, that library gives you most of the same scratch functionality (like the rendering) but it's a little bit easier to work with, because it has less scratch-specific code (like things that interact with scratch-gui).
Whichever way you decide to go, I wish you the best of luck with your project :D It sounds like a fun one!
--Beka