USB HID Joystick

how can use 16 axis to joystick, i no need more than all analog input .
how many can add, i read before at 16 analog joystick axis have possiple one arduino mega 2560 board, but no understand how made ?
how make descriction ?

what different have mega board if have ch340 chip, 16U2 chip or new 8U2 chip to board ?

what can use easy whit mega-joy or own usb-hid description ?
and have somebody ready description maximum axis and no more need.
better if have all 16 axis analog input. but maximimum what can add.
my flight sim fsx need only analog axis.