Frontend choice was basically pre-ordained to be React. Seems like a strong choice on merits alone, plus I needed to learn it to stay current. I never liked Redux.js from the first time I tried to work with it, but a mate had recommended MobX and after watching a few videos I felt like I could fit the mental model of hit in my head. Using Material-UI which is a great timesaver and make sure I throw a few bucks their way every month via the open source collective.
Defaulted to Rails with PostgreSQL just because that's where my past strength as a dev had been. First prototype was in Go but was struggling a bit with the quality of libraries I needed so I went back to old faithful.
As soon as TypeScript was supported by default in Create React App I ported everything over. That combined with swagger code gen has given me really good type safety from the API boundary and above. I semi-regret the Go/Rails decision because I miss the type safety despite pain points with libraries.
I will probably look to flip back to Go gradually (probably via lambda) at a point where it makes sense for the business.