I don’t know if there’s any documentation about this, I think a lot of people prefer to start converting their business logic (the core of the architecture), and keep the outer layers in the language they used before (JS, TS, etc). You can start converting a file, compare the generated code with the original JS file, run the same tests on it, this way you can be pretty confident your conversion went ok, and then you can continue the conversion.
If you use TS today, genType can help you interface easily with your existing TS code base.
It would help if you gave more details about your use case, the language you use today, the frameworks, the main tools, etc.
We have quite many power users with more experience than me on converting projects to rescript, they’ll likely chime in 
edit: you can take a look at this small guide for converting a file from JS.