For part of your project, you want a random number and or letter generator. App Inventor has the blocks. use the random aset seed block and the random block in the Math blocks doing something like in this
These characters could be put in a list and you could then use the pick a random item (this is a List block) from the list say eight times to make an 8 character random password.
There will probably be others posting other ideas. Good luck.
Regards,
Steve