I'm using the official Raspberry Pi 7" touchscreen, but since it's rather expensive, I'm wondering what to look for (and look out for) in a touchscreen for the Pi 3 (or Raspberry Pis in general).
Simply search for keyword ' 7" LCD Rapberry Pi ' in ebay, you will get a list of them. Contact sellers before purchase, make sure they have instruction to make it work on the latest RPi firmware, or else you may end up with a product that supports earlier version only.
Yes, the raspberry pi will work with any screen or display unit as long as it has an HDMI port. suppose if you computer pc display has DVI-D display, You can buy a converter of HDMI to DVI-D.