Aside from all the good and valid comments about reducing scope and shipping an MVP, I'd like to raise another point which may be controversial (or even wrong), but still worth raising:
Would it have been different if you had used Rails? A few of the problems you mention (rich text editing, validation, and to some extend, pdf exports) are very easily solved in Rails. Take rich text editing: It's literally a couple minutes to use ActionText. Or validations / forms, there's really not much work to do. PDF exports are also not too hard via wicked_pdf [1] if you're okay with fixing some formatting quirks later on.
I've seen both worlds by writing tons of JS / React code myself, and at that time (2016-2018) those problems were almost an order of magnitude more time-costly to implement in SPAs. I remember react-router.. not great memories.
Of course, all the points reducing MVP scope still hold, but.. if you could have had all those features (nearly) for free, would you be at another stage now? Who knows.