Also, if someone is ambidextrous, how do they pick which hand does what??
you'll probably play whatever instrument you have. and if you literally have exactly equal choice between the two, then you would probably weigh the advantages and disadvantages, some of which might be: right handed instruments will usually be easier to find. playing lefty will look more unique. playing the opposite way of the way the instrument was intended may make your playing very unique, yet that will also possibly create some slight blockades in communication when discussing playing technique with others who don't also play backwards