I would recommend buying the CD version for the userpatch. There is a patch to turn HD Edition into the CD version but then you cannot use HD Edition while that patch is installed.
The scenario FAQ is somewhat outdated and old looking, but much of it still works. For example I found a great trigger system from oliver in 2006 for inverted object detection which solved all my problems in my RiverRaids scenarios. Just ask questions freely in the scenario design thread, and find the trigger studio thread in the mods forum for those questions too.
"Excellent could be any map that has the quality of a ES random map or ES scenario. AoK is an excellent, award winning game. That's where I'd start." -AnastasiaKafka
"Hard work is evil. Bitmaps are stupid. Working on a scenario for more than one afternoon is stupid. Triggers are stupid. Testing your own scenario is stupid. The world is stupid. You are the Greatest." -Ingo Van Thiel