Well, having a working lexer/parser is needed to make a compiler, but I see very little reason to write your own parser. Lexer yeah, but from what I've heard parsers are tedious and better optimized by programs.
Anyway, thing that helps me do stuff - focus on getting a piece of program right. Then move onto another part.
Another good saying, all good software starts simple and evolves into a complex solution. So maybe start with Lisp syntax and evolve it into something more complex, when you're ready.
Interestingly there is another article by Walter Bright on writing your own compiler on DrDobbs [1] in which he explicitly recommends to write the parser yourself and I have received similar advice by others that know how to implement compilers. My personal experience in implementing a subset of C turned out similar.
Anyway, thing that helps me do stuff - focus on getting a piece of program right. Then move onto another part.
Another good saying, all good software starts simple and evolves into a complex solution. So maybe start with Lisp syntax and evolve it into something more complex, when you're ready.