Here is what I have to offer for advice.
The network drivers may be a problem because ralink and realtek aren't too good about open distributing linux based drivers. Community based stiros have the greatest problem with this because they have not negotiated licensing deals with those companies to use the drivers and firmware, so you best bet would be to start with a commercial distro like Ubuntu, Fedora, RedHat, Novell SUSE, etc..
To give you the user interface option you wish to get you can run xterm on top of the X window manager and have your custom application set to start on GUI startup. This will present you with your application and a terminal in the background for crash handling. However it may be possible to just have X11 to boot with the application started only, I just haven't tested it.
You can disable or blacklist the keyboard driver modules, but if network communication is ever lost (such as the network card dying) then the box would be dead without any way to physically access and update it for new hardware. I am also unsure if the keyboard modules would be necessary for remote command to be accepted. I would recommend physically blocking the keyboard and usb ports so they cannot be accessed by the users as a simplified method.
The kernel and X11 window system have support for various touchscreen interfaces so that shouldn't be very difficult.
For this to be safely implemented you will have to consider if the remote access with be GUI or CLI based, then install the necessary services, security mechanisms and firewall logic to keep it secure.
You also must advise whoever will developing this platform of the type of consumers and industry this will be distributed to so they can adjust the access methods and security to best fit the needs and capabilities of the users.
Now for this project I would normally be willing to experiment to see if I can get it working, but without the physical hardware and necessary software I cannot reliably give you any configuration or installation files. Your best bet would be to contact a contract development firm and supply them with the necessary hardware and software for them to build and test your goal platform.