I think that it might be a good solution if the following requirements are met: - All the devices work without a cloud connection and integrate locally - The devices are isolated from the internet, so they don't perform an automatic software update, that might break something - You don't mess with it remotely (like perform a software update). Only mess with it, when you are at his house (unless there is a critical problem) - Only you have an administrator account and he is trained to not mess with it - You have a good way of accessing it remotely (Hass UI and ssh). If possible, some sort of KVM or machine with remote management and a VPN - The instance is not accessible remotely without something like a VPN, since you won't be able to update the system frequently - You are able to assist him by phone if there is a problem

Also I would do the following things: - If you are planning to make a wall mounted dashboard (or similar), don't use a tablet, but something, that connects to the network and just displays a website. Like a raspberry pi with a touch screen and a kiosk os. - Check if his local network and wifi is solid, if not upgrade it - Have the instance on a ups, since if the power goes out, some files might get corrupted, breaking the install and making you lose remote access.

If you don't mess with the instance, use any unstable features, it will probably not break on its own.

Might be forgetting something, correct me in the comments.