Even if I was a *illionaire I’d rather gargle lava rocks than touch Oracle with a mile long pole

This looks interesting, though a mighty undertaking. Any reason why not take an existing project and fork it? Or even just an ERPNext module? Would help cover a bunch of potential issues rather than start from scratch. Alternatively, have you thought of what would the MVP be to test it out? That way won’t fall into the do-everything-now trap (been there, done that, don’t recommend). Also, it looks very US-centric, so not gonna ask about GDPR, data security, etc. Instead, re: FE - for prototyping, don’t need design, just functional HTML + forms. Or, can try and poke at some premade or quick-assemble templates. Have you thought about functional (not design) requirements for the user experience, AKA how you imagine the users of this would use it? That is, full day in the office VS checking it once-monthly VS yearly for taxes, etc.