What's currently in your JavaScript stack? I'm probably going to suggest getting rid of most of it if possible so that you can focus on your code. Here's a dirty secret: you probably don't need a JS build system or anything from ES2015+ if you don't feel like learning it yet[0]. If you're using React, you probably don't need to integrate any of the latest tech like Redux and tcomb-form and all those other super cool innovations. You can even get away with using Node modules in the old-fashioned "link to a script file" way[1]. Sure, someone can claim that each of those tools serves a purpose and can prevent a whole class of headaches that might happen. What they won't say is that trying to wrangle them all together right away is causing you a bigger headache than any of the others!
I'm working on an application that has about 15K lines of hand-prepared React/Flux JavaScript (well, TypeScript) and it is planned to scale up by maybe an order of magnitude eventually. It's built with ES5 and plain old revealing modules. I'm managing dependencies by hand. I'm not using Node or CommonJS modules at all. Heck, I'm not even using JSX yet because my version of Visual Studio doesn't have TSX (TypeScript+JSX) built in. Does this mean some headaches and extra labor? Sure! Do I feel like an imposter when reading about all this awesome fancy new stuff? Sometimes!
But the headaches are surprisingly minor and barely figure in most of the time. If/when these headaches get bigger (I suspect this will start in earnest when more front-end developers join the project), then I'll take another look at integrating a module loader, or a form generator, or an automagic React router, or a super-cool atomic state system like Redux. In case you're wondering the application works amazingly well and most of the time implementing even far-out crazy features has been easy and fun.
Finally, don't get too worried about making the "wrong" choices, and don't bail out for something newer when you hit your first roadblock. Most of the options you have available these days work great! The things we expect them to do are totally incredible, that's the only reason people are still proposing alternatives all the time.
[0]If you don't need to support older browsers, ES2015 is pretty easy to include. Otherwise if you need to use examples based on an ES2015+ version, just paste the code into the Babel REPL: https://babeljs.io/repl/
[1]You can get any bundled npm module here: https://wzrd.in/