Always use a solid state drive - SSD.
Lack of space should be supplemented with a low cost ultra fit usb flash drive.
CPU and memory should be sufficient to allow for the use of following applications in parallel:
VOIP (voice over IP) with screen sharing and/or and screen recording. For ex: skype, hipchat, zoom.us, google hangouts, webex, slack, joinme etc.
Browsers with multiple tabs and/or sessions
We recommend Apple 13 inch macbook air
roughly 1,000 USD