Debugging React has been pretty painless. Errors show up in the console, step through with Devtools if things get weird... One of the great things about React is It's Just Javascript (technically CoffeeScript in my case).
One thing that has made things a bit easier is React Developer Tools: https://chrome.google.com/webstore/detail/react-developer-to...
It gives you a Devtools tab that looks like the DOM Inspector, but it's the React component tree. I've mostly found it helpful when dealing with abstract components (components that render other top-level components rather than DOM components).
I can't see your code so unfortunately I can't give you more specific advice, but in general, I've found that if you feel like you have too much code, you're probably overcomplicating things. This holds true in React, and (in my experience) programming in general. Then again, if it's just a big form, that could be the problem. Big forms aren't usually a great UX anyways, so maybe consider breaking that up into more discrete pieces - but I'm basically talking out of my ass at this point since I don't know your situation.
Hope this helps though! Also happy to answer any questions over email (in my profile). I'm far from a React expert but always glad to lend a hand.