When it comes to libraries, I would recommend sticking with built-in features for tasks like image loading or parsing. This actually works quite well, and there's no need to delve into external solutions, especially for prototyping. Dart's factory methods come in handy for parsing JSON from an API, and the internal HTTP package is also very well done (for more advanced stuff there is a package called dio).
The main challenge lies in state management. Be sure to choose the right external stuff. The 'bloc' package seems to be the state of the art at the moment, but if you prefer something simpler, Provider is the way to go. The need for other libraries may become apparent after spending some time on the project.
Flutter is a great choice for quick prototyping. You can build something in a matter of minutes. Many people prefer this way over launching Figma, which says a lot :)
I know the old Java based Android and the old obj-c based ios but haven't bothered to get fresh on all the changes of the last 5 years (swift, kotlin, jetpack, etc). I have been considering the Flutter option as a cross-platform way to do quick prototyping. Any good learning resources you can suggest (books, sites, tutorials)? Any particular libraries (e.g. image loading/rendering, parsing, etc.) you can suggest? Anything to avoid that seemed low value?