I have been relying on cheap computers from ebay for running machines, as you can get complete 'refurbed' setups for under a hundred, and I'd rather have the computer near the machine than that far away.

The key thing with touchscreens, is stick to resistive screens as they rely on surface pressure, so are not affected by contamination like capacitive screens are. Resistive is generally not as accurate though, so you need to have the ability to have reasonably sized buttons.

Mistakes are part of the fun, however experience has taught to me try and make them in the cheapest/easiest way possible..