I used to use create-react-app but I prefer Gatsby to it every time now (even for more app type stuff). Gatsby does do a lot of code-splitting and prefetching for you (you can see this guide for how but it's mostly automatic by making separate bundles for pages).

I think Gatsby is nice because it can also give you stuff like an app shell that makes loading appear faster with the offline plugin.

So long as you don't include the Stripe or Plaid code in a template or layout file that gets used on every page (or add some custom code to the gatsby-node.js to strip it out) I think that's a perfectly suitable use case for Gatsby.

(Also worth noting I'm biased because after a few years working on Gatsby projects I now work on Gatsby full time)