Nice to see another visual impairment inventor like myself I'm working on a visual awareness system that latches onto your standard white cane. I would suggest for your tactile buttons you make sure each button each has above or on top of it. Braille to represent what each button represents that way it will be alot easier for your client to use instead of fiddling around trying to figure out what each button does.
Extra addition would to make some instructions which are in braille also should your client forget how to use it or want to show their friends.
This seems similar and might help. Always worth posting on Electronics.Stackexchange and raspberry/arduino subreddits on reddit
https://www.reddit.com/r/raspberry_pi/c ... pberry_pi/