[alan lacey] “Is it possible to render frame numbers to previews somehow?”
Check off Frame in the HUD settings and then set Render HUD in Render Settings/Options – or use Xpresso to send the frame number to a Text Spline (and obviously, put that in an Extrude or Loft).
[alan lacey] “Also how do I abort a preview render, some of these can be very prolonged”
Start another Preview (which will ask to stop the current one)