I imagine that stuffing an RPi into a box in a badly ventilated area might cause some heating issues. They run hot and are not really rated to handle that long-term.
More generally, if you're looking at POS systems, the new hotness is to just use a tablet. Solves the display problem quite easily. USB barcorde scanners usually work as keyboards, so it's not hard to get set up.
If you're looking to do it with a Pi, there are small screens for the device, but I think the parts total will quickly get higher than a low-end Android tablet.
Tablet's get expensive pretty quickly, and they will break. I need at least five EPOSs for "reasons". And I reckon I could have every thing I need, plus replacement hardware on location for a fraction of the cost of using tablets.
I don't mean to sound dismissive (building your own stuff is a good exercise in minimalism) but whatever you're building has a decent likelihood to break as well.
Think about having a custom linux setup compared to Windows. There's some extra stability in one angle, but your wifi stops working every full moon and your keyboard layout gets randomized on reboot.
Though the advantage of building it yourself is that you can replace more specific parts.
More generally, if you're looking at POS systems, the new hotness is to just use a tablet. Solves the display problem quite easily. USB barcorde scanners usually work as keyboards, so it's not hard to get set up.
If you're looking to do it with a Pi, there are small screens for the device, but I think the parts total will quickly get higher than a low-end Android tablet.