Architecture and protocol question, connecting my electrical wiring

I would like to lead my existing home installations to openhab.
Mainly, I have an analog control panel at home, comprising about 4 shutters for blinds, 4 traditional switches and a DALI controller for dimmable LED spots.

The architecture I envisage is as follows:

  • An Arduino controls switches for blinds and mimics the DALI protocol.
  • An old android phone serves as a terminal for the android, which should be connected by USB and communicate by some sort of serial protocol. I find it important that the system Android phone/Arduino is 100% stand alone. Not relying on any wireless connection or other running servers.
  • The phone can then use Wifi (or bluetooth, if wifi is not available) to talk to the openhab server
    You can find a schematics of the setup here:

Questions: Is there an intelligent convention for the serial communication between the Arduino and the phone, or should I just make something up?
Second thing thats bothering me: Is there a way I do not need to create a GUI for the app handling the communication? Is there something existing or can the existing apps be used?

I think you’re putting a wrong focus, leading to a questionable architecture and pretty unique implementation … that will not allow you to profit from existing implementations for bindings etc, and that noone will be able to help you with as it’s all proprietary and unique.
How often is a server supposed to fail ? How often is wireless transmission to fail ? And how bad is that if you’re honest to yourself ?
I’d well use wireless actuators to run the blinds, and connect the old switches there, too, so even should your server or wireless transmission fail, you’d still be able to manually operate the blinds.
There’s WiFi and ZWave actuators many people here successfully use for the purpose.
[well of course you can also wire them to your server in a number of ways but most people to retrofit houses don’t want to put new wires everywhere so I assume you don’t want that]