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If you've knowledge in Python, I would do a prototype using Kivy which allows you to develop rapid applications using Python and Pygame and it has very descent widgets as you can see in the demo app.
Once your product is validated, I would consider native development for every platform if it is necessary.
At this point, what it matters most is the idea validation, i.e. if there's someone willing to use or pay your product, so speed to deliver and speed over iterations is the most important thing.
Lastly, if you've not already, I would read Lean Startup by Eric Ries. It could save you several months.
I wish you the best!
It may not be necessary to update the book as Kivy ages pretty well. For example, the Android version of the Kivy Showcase demo was published in January 2016 and required Android 2.2 or later. Almost 4 years later it still works with Android 10, and even on Chrome OS devices with Android support.