Came here to say it looks like JSON Builder step can handle Integers being passed and tagged as number fields successfully, but JSON Parser step doesn't let you specify a number field - everything is a string, array or object 😞
Also another observation - JSON Builder (and Flow Designer in general) doesn't seem to be able to allow the developer to choose whether a Choice field pill will return the Choice Label or Value. I would LOVE to be able to do this and use JSON builder to return the choice integer value for integrations that them.
Another observation is that JSON Builder doesn't seem to be able to convert a Currency field to a decimal number - it leaves it as a string with a currency character (recognising how tricky currencies can be, I'll let this one slide) 🙂
My solution to all this is to pass my reference object into a Script step to do all the Choice value conversions against the sys_choice table and to also pass my currency values so they can be transformed.
