You can't just connect a VGA screen to HDMI or vice versa as HDMI is digital and VGA is an analogue signal. You can buy converter boxes to do this for you. The best option to run a VGA screen of that GPU is to use a DVI-VGA adaptor as DVI connectors can carry an analogue signal for VGA screens (much cheaper option that getting a HDMI converter).
it really depends, this has been tested Which Analog is the older way of video signal, Digital is better but doubt you will actually notice it. For most people you can't tell the difference.