Dan. As I remember the onboard editor is a tad buggy.  You will probably know it will only work in Windows mode. The sim might crash when you place the objects but they should be there when you restart it. Not sure about runways.

I find Chuck Dome's Static Object Designer v.1.2 much more reliable. http://www.simviation.com/cfs1utilitites2.htm
It will do much the same as the onboard editor but does not have a graphics interface. You will need to go to the area in Free Flight & slew around to note the exact co-ords. It's a while since I've done this in CFS1. I think you can use MkAFD for creating new runways & menu entries. http://www.mnwright.btinternet.co.uk/programs/tools.htm

Dan. To make the cliffs you could try CfsTMap. http://www.mnwright.btinternet.co.uk/programs/cfstmap.htm  I don't know how easy it is to use as haven't done this in CFS1. MW's stuff is usually first class. There might be other similar utilities around.
For the menu entries use MkAFD from my previous link.