Woah thanks :)!
We had previous experience with writing a compiler for subset of C (during uni), and I also did some learning from the "Crafting Interpreters" book, but regarding the DSL design, I would say it is actually simpler -> we just went kind of ad-hoc and are expanding syntax as we figure out what we need. I am not sure if that is the best process, I would love to learn about the better one if there is one, but it worked so far. Wasp is still pretty simple, really not much more expressive than JSON at the moment, but we hope to add more stuff soon.
While we are using parser combinators right now to parse the language, which is pretty manual process, once it becomes clearer what the language looks like, we will look into capturing it with formal grammar and then use some of the more advanced tools to parse it.
The book I am going through right now is "Language Implementation Patterns" by creator of Antlr, it has chapters specific for designing DSLs!
we also have a DSL design channel in our Discord - feel free to join and start the discussion, we'd be happy to learn from you and also help if we can! https://discord.com/invite/rzdnErX